From a7e23a531c9f35ad804e3ae161ac0179745a6888 Mon Sep 17 00:00:00 2001
From: Fredrik Roubert <roubert@google.com>
Date: Tue, 23 Apr 2024 14:45:10 +0200
Subject: [PATCH] ICU-22721 Clang-Tidy: modernize-use-override

https://releases.llvm.org/17.0.1/tools/clang/tools/extra/docs/clang-tidy/checks/modernize/use-override.html
---
 .../source/layoutex/layout/ParagraphLayout.h  |  6 +-
 icu4c/source/layoutex/layout/RunArrays.h      | 20 +++---
 icu4c/source/layoutex/plruns.cpp              |  6 +-
 .../samples/translit/answers/unaccent.h       |  8 +--
 icu4c/source/samples/translit/unaccent.h      |  8 +--
 .../source/test/letest/PortableFontInstance.h | 30 ++++----
 icu4c/source/test/letest/SimpleFontInstance.h | 28 ++++----
 icu4c/source/test/letest/cmaps.h              |  4 +-
 .../test/perf/DateFmtPerf/DateFmtPerf.h       | 50 ++++++-------
 icu4c/source/test/perf/charperf/charperf.h    | 14 ++--
 icu4c/source/test/perf/collperf/collperf.cpp  | 24 +++----
 .../source/test/perf/collperf2/collperf2.cpp  | 70 +++++++++----------
 .../test/perf/dicttrieperf/dicttrieperf.cpp   | 20 +++---
 .../perf/howExpensiveIs/howExpensiveIs.cpp    | 42 +++++------
 .../test/perf/leperf/PortableFontInstance.h   | 30 ++++----
 .../test/perf/leperf/SimpleFontInstance.h     | 28 ++++----
 icu4c/source/test/perf/leperf/cmaps.h         |  4 +-
 .../test/perf/localecanperf/localecanperf.cpp | 10 +--
 icu4c/source/test/perf/normperf/dtfmtrtperf.h |  6 +-
 icu4c/source/test/perf/normperf/normperf.h    | 10 +--
 .../test/perf/normperf/simplenormperf.cpp     |  4 +-
 .../test/perf/strsrchperf/strsrchperf.h       |  6 +-
 icu4c/source/test/perf/ubrkperf/ubrkperf.h    | 16 ++---
 .../test/perf/unisetperf/draft/bitset.cpp     |  2 +-
 .../test/perf/unisetperf/draft/trieset.cpp    |  2 +-
 .../test/perf/unisetperf/unisetperf.cpp       | 16 ++---
 icu4c/source/test/perf/usetperf/usetperf.cpp  | 10 +--
 icu4c/source/test/perf/ustrperf/stringperf.h  | 12 ++--
 icu4c/source/test/perf/utfperf/utfperf.cpp    | 10 +--
 .../test/perf/utrie2perf/utrie2perf.cpp       | 10 +--
 30 files changed, 253 insertions(+), 253 deletions(-)

diff --git a/icu4c/source/layoutex/layout/ParagraphLayout.h b/icu4c/source/layoutex/layout/ParagraphLayout.h
index f6167ae3292..4efca1fb03e 100644
--- a/icu4c/source/layoutex/layout/ParagraphLayout.h
+++ b/icu4c/source/layoutex/layout/ParagraphLayout.h
@@ -156,7 +156,7 @@ public:
          *
          * @stable ICU 3.2
          */
-        virtual inline UClassID getDynamicClassID() const { return getStaticClassID(); }
+        inline UClassID getDynamicClassID() const override { return getStaticClassID(); }
 
     private:
 
@@ -319,7 +319,7 @@ public:
          *
          * @stable ICU 3.2
          */
-        virtual inline UClassID getDynamicClassID() const { return getStaticClassID(); }
+        inline UClassID getDynamicClassID() const override { return getStaticClassID(); }
 
     private:
 
@@ -550,7 +550,7 @@ public:
      *
      * @stable ICU 3.2
      */
-    virtual inline UClassID getDynamicClassID() const { return getStaticClassID(); }
+    inline UClassID getDynamicClassID() const override { return getStaticClassID(); }
 
 private:
 
diff --git a/icu4c/source/layoutex/layout/RunArrays.h b/icu4c/source/layoutex/layout/RunArrays.h
index 08e32826642..69d57a0ebed 100644
--- a/icu4c/source/layoutex/layout/RunArrays.h
+++ b/icu4c/source/layoutex/layout/RunArrays.h
@@ -161,7 +161,7 @@ public:
      *
      * @stable ICU 3.2
      */
-    virtual inline UClassID getDynamicClassID() const { return getStaticClassID(); }
+    inline UClassID getDynamicClassID() const override { return getStaticClassID(); }
 
 protected:
     /**
@@ -361,11 +361,11 @@ public:
      *
      * @stable ICU 3.2
      */
-    virtual inline UClassID getDynamicClassID() const { return getStaticClassID(); }
+    inline UClassID getDynamicClassID() const override { return getStaticClassID(); }
 
 protected:
-    virtual void init(le_int32 capacity);
-    virtual void grow(le_int32 capacity);
+    void init(le_int32 capacity) override;
+    void grow(le_int32 capacity) override;
 
 private:
 
@@ -498,11 +498,11 @@ public:
      *
      * @stable ICU 3.2
      */
-    virtual inline UClassID getDynamicClassID() const { return getStaticClassID(); }
+    inline UClassID getDynamicClassID() const override { return getStaticClassID(); }
 
 protected:
-    virtual void init(le_int32 capacity);
-    virtual void grow(le_int32 capacity);
+    void init(le_int32 capacity) override;
+    void grow(le_int32 capacity) override;
 
     /**
      * @internal
@@ -635,11 +635,11 @@ public:
      *
      * @stable ICU 3.2
      */
-    virtual inline UClassID getDynamicClassID() const { return getStaticClassID(); }
+    inline UClassID getDynamicClassID() const override { return getStaticClassID(); }
 
 protected:
-    virtual void init(le_int32 capacity);
-    virtual void grow(le_int32 capacity);
+    void init(le_int32 capacity) override;
+    void grow(le_int32 capacity) override;
 
 private:
 
diff --git a/icu4c/source/layoutex/plruns.cpp b/icu4c/source/layoutex/plruns.cpp
index e2796ad24d2..2bae89fb2bd 100644
--- a/icu4c/source/layoutex/plruns.cpp
+++ b/icu4c/source/layoutex/plruns.cpp
@@ -301,11 +301,11 @@ public:
      *
      * @draft ICU 3.8
      */
-    virtual inline UClassID getDynamicClassID() const;
+    inline UClassID getDynamicClassID() const override;
 
 protected:
-    virtual void init(le_int32 capacity);
-    virtual void grow(le_int32 capacity);
+    void init(le_int32 capacity) override;
+    void grow(le_int32 capacity) override;
 
 private:
 
diff --git a/icu4c/source/samples/translit/answers/unaccent.h b/icu4c/source/samples/translit/answers/unaccent.h
index 839d4a95df8..ca45a6b5840 100644
--- a/icu4c/source/samples/translit/answers/unaccent.h
+++ b/icu4c/source/samples/translit/answers/unaccent.h
@@ -29,7 +29,7 @@ class UnaccentTransliterator : public Transliterator {
      */
     virtual ~UnaccentTransliterator();
 
-    virtual UClassID getDynamicClassID() const override;
+    UClassID getDynamicClassID() const override;
     U_I18N_API static UClassID U_EXPORT2 getStaticClassID();
 
  protected:
@@ -37,9 +37,9 @@ class UnaccentTransliterator : public Transliterator {
     /**
      * Implement Transliterator API
      */
-    virtual void handleTransliterate(Replaceable& text,
-                                     UTransPosition& index,
-                                     UBool incremental) const;
+    void handleTransliterate(Replaceable& text,
+                             UTransPosition& index,
+                             UBool incremental) const override;
 
  private:
 
diff --git a/icu4c/source/samples/translit/unaccent.h b/icu4c/source/samples/translit/unaccent.h
index aa27a56dd2a..69037332a54 100644
--- a/icu4c/source/samples/translit/unaccent.h
+++ b/icu4c/source/samples/translit/unaccent.h
@@ -32,9 +32,9 @@ class UnaccentTransliterator : public Transliterator {
     /**
      * Implement Transliterator API
      */
-    virtual void handleTransliterate(Replaceable& text,
-                                     UTransPosition& index,
-                                     UBool incremental) const;
+    void handleTransliterate(Replaceable& text,
+                             UTransPosition& index,
+                             UBool incremental) const override;
 
  private:
 
@@ -83,7 +83,7 @@ public:
      * different class IDs.
      * @stable ICU 2.0
      */
-    virtual UClassID getDynamicClassID() const { return getStaticClassID(); };
+    UClassID getDynamicClassID() const override { return getStaticClassID(); };
 
 private:
 
diff --git a/icu4c/source/test/letest/PortableFontInstance.h b/icu4c/source/test/letest/PortableFontInstance.h
index a8d86348883..9405674ed18 100644
--- a/icu4c/source/test/letest/PortableFontInstance.h
+++ b/icu4c/source/test/letest/PortableFontInstance.h
@@ -66,14 +66,14 @@ private:
 
 protected:
     const void *readFontTable(LETag tableTag) const { size_t ignored; return readFontTable(tableTag, ignored); }
-    const void *readFontTable(LETag tableTag, size_t &length) const;
+    const void *readFontTable(LETag tableTag, size_t &length) const override;
 
 public:
     PortableFontInstance(const char *fileName, float pointSize, LEErrorCode &status);
 
     virtual ~PortableFontInstance();
 
-    virtual const void *getFontTable(LETag tableTag, size_t &length) const;
+    const void *getFontTable(LETag tableTag, size_t &length) const override;
 
     virtual const char *getNameString(le_uint16 nameID, le_uint16 platform, le_uint16 encoding, le_uint16 language) const;
 
@@ -83,39 +83,39 @@ public:
 
     virtual void deleteNameString(const LEUnicode16 *name) const;
 
-    virtual le_int32 getUnitsPerEM() const;
+    le_int32 getUnitsPerEM() const override;
 
     virtual le_uint32 getFontChecksum() const;
 
     virtual le_uint32 getRawChecksum() const;
 
-    virtual le_int32 getAscent() const;
+    le_int32 getAscent() const override;
 
-    virtual le_int32 getDescent() const;
+    le_int32 getDescent() const override;
 
-    virtual le_int32 getLeading() const;
+    le_int32 getLeading() const override;
 
     // We really want to inherit this method from the superclass, but some compilers
     // issue a warning if we don't implement it...
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper, le_bool filterZeroWidth) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper, le_bool filterZeroWidth) const override;
     
     // We really want to inherit this method from the superclass, but some compilers
     // issue a warning if we don't implement it...
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper) const override;
 
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch) const override;
 
-    virtual void getGlyphAdvance(LEGlyphID glyph, LEPoint &advance) const;
+    void getGlyphAdvance(LEGlyphID glyph, LEPoint &advance) const override;
 
-    virtual le_bool getGlyphPoint(LEGlyphID glyph, le_int32 pointNumber, LEPoint &point) const;
+    le_bool getGlyphPoint(LEGlyphID glyph, le_int32 pointNumber, LEPoint &point) const override;
 
-    float getXPixelsPerEm() const;
+    float getXPixelsPerEm() const override;
 
-    float getYPixelsPerEm() const;
+    float getYPixelsPerEm() const override;
 
-    float getScaleFactorX() const;
+    float getScaleFactorX() const override;
 
-    float getScaleFactorY() const;
+    float getScaleFactorY() const override;
 
 };
 
diff --git a/icu4c/source/test/letest/SimpleFontInstance.h b/icu4c/source/test/letest/SimpleFontInstance.h
index 521cb8886bf..471a029d1e4 100644
--- a/icu4c/source/test/letest/SimpleFontInstance.h
+++ b/icu4c/source/test/letest/SimpleFontInstance.h
@@ -36,37 +36,37 @@ public:
 
     virtual ~SimpleFontInstance();
 
-    virtual const void *getFontTable(LETag tableTag, size_t &length) const;
+    const void *getFontTable(LETag tableTag, size_t &length) const override;
 
-    virtual le_int32 getUnitsPerEM() const;
+    le_int32 getUnitsPerEM() const override;
 
-    virtual le_int32 getAscent() const;
+    le_int32 getAscent() const override;
 
-    virtual le_int32 getDescent() const;
+    le_int32 getDescent() const override;
 
-    virtual le_int32 getLeading() const;
+    le_int32 getLeading() const override;
 
     // We really want to inherit this method from the superclass, but some compilers
     // issue a warning if we don't implement it...
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper, le_bool filterZeroWidth) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper, le_bool filterZeroWidth) const override;
     
     // We really want to inherit this method from the superclass, but some compilers
     // issue a warning if we don't implement it...
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper) const override;
 
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch) const override;
 
-    virtual void getGlyphAdvance(LEGlyphID glyph, LEPoint &advance) const;
+    void getGlyphAdvance(LEGlyphID glyph, LEPoint &advance) const override;
 
-    virtual le_bool getGlyphPoint(LEGlyphID glyph, le_int32 pointNumber, LEPoint &point) const;
+    le_bool getGlyphPoint(LEGlyphID glyph, le_int32 pointNumber, LEPoint &point) const override;
 
-    float getXPixelsPerEm() const;
+    float getXPixelsPerEm() const override;
 
-    float getYPixelsPerEm() const;
+    float getYPixelsPerEm() const override;
 
-    float getScaleFactorX() const;
+    float getScaleFactorX() const override;
 
-    float getScaleFactorY() const;
+    float getScaleFactorY() const override;
 
 };
 
diff --git a/icu4c/source/test/letest/cmaps.h b/icu4c/source/test/letest/cmaps.h
index 875bb97ee24..f5580d0d84f 100644
--- a/icu4c/source/test/letest/cmaps.h
+++ b/icu4c/source/test/letest/cmaps.h
@@ -40,7 +40,7 @@ public:
 
     virtual ~CMAPFormat4Mapper();
 
-    virtual LEGlyphID unicodeToGlyph(LEUnicode32 unicode32) const;
+    LEGlyphID unicodeToGlyph(LEUnicode32 unicode32) const override;
 
 protected:
     CMAPFormat4Mapper() {};
@@ -61,7 +61,7 @@ public:
 
     virtual ~CMAPGroupMapper();
 
-    virtual LEGlyphID unicodeToGlyph(LEUnicode32 unicode32) const;
+    LEGlyphID unicodeToGlyph(LEUnicode32 unicode32) const override;
 
 protected:
     CMAPGroupMapper() {};
diff --git a/icu4c/source/test/perf/DateFmtPerf/DateFmtPerf.h b/icu4c/source/test/perf/DateFmtPerf/DateFmtPerf.h
index d41dcc55e03..37456d5eee0 100644
--- a/icu4c/source/test/perf/DateFmtPerf/DateFmtPerf.h
+++ b/icu4c/source/test/perf/DateFmtPerf/DateFmtPerf.h
@@ -61,7 +61,7 @@ public:
 	BreakItFunction(){num = -1;}
 	BreakItFunction(int a, bool b){num = a; wordIteration = b;}
 
-	virtual void call(UErrorCode * status)
+	void call(UErrorCode* status) override
 	{		
 		BreakIterator* boundary;
 
@@ -102,7 +102,7 @@ public:
 
 	}
 
-	virtual long getOperationsPerIteration()
+	long getOperationsPerIteration() override
 	{
 		if(wordIteration) return 125*num;
 		else return 355*num;
@@ -161,7 +161,7 @@ public:
         strcpy(locale, loc);
 	}
 
-	virtual void call(UErrorCode* status)
+	void call(UErrorCode* status) override
 	{
 
 		UErrorCode status2 = U_ZERO_ERROR;		
@@ -208,7 +208,7 @@ public:
 		//u_cleanup();
 	}
 
-	virtual long getOperationsPerIteration()
+	long getOperationsPerIteration() override
 	{
 		return NUM_DATES * num;
 	}
@@ -250,7 +250,7 @@ public:
                 strcpy(locale, loc);
         }
 
-        virtual void call(UErrorCode* /* status */)
+        void call(UErrorCode* /*status*/) override
         {
 
                 Locale loc(locale);
@@ -263,7 +263,7 @@ public:
                 }
         }
 
-        virtual long getOperationsPerIteration()
+        long getOperationsPerIteration() override
         {
                 return num;
         }
@@ -289,7 +289,7 @@ public:
         strcpy(locale, loc);
         }
 
-        virtual void call(UErrorCode* /* status */)
+        void call(UErrorCode* /*status*/) override
         {
                 Locale loc(locale);
                 UErrorCode status2 = U_ZERO_ERROR;
@@ -302,7 +302,7 @@ public:
                 delete fmt;
         }
 
-        virtual long getOperationsPerIteration()
+        long getOperationsPerIteration() override
         {
                 return num;
         }
@@ -336,7 +336,7 @@ public:
         strcpy(locale, loc);
 	}
 
-	virtual void call(UErrorCode* /* status */)
+	void call(UErrorCode* /*status*/) override
 	{
 		UErrorCode status2 = U_ZERO_ERROR;		
 		Calendar *cal;
@@ -357,7 +357,7 @@ public:
                 delete cal;
 	}
 
-	virtual long getOperationsPerIteration()
+	long getOperationsPerIteration() override
 	{
 		return num;
 	}
@@ -391,7 +391,7 @@ public:
         strcpy(locale, loc);
 	}
 
-	virtual void call(UErrorCode* /* status */)
+	void call(UErrorCode* /*status*/) override
 	{
 		Locale loc(locale);
                 UnicodeString tzname("UTC");
@@ -401,7 +401,7 @@ public:
                 }
 	}
 
-	virtual long getOperationsPerIteration()
+	long getOperationsPerIteration() override
 	{
 		return num;
 	}
@@ -435,7 +435,7 @@ public:
         strcpy(locale, loc);
 	}
 
-	virtual void call(UErrorCode* /* status */)
+	void call(UErrorCode* /*status*/) override
 	{
 		UErrorCode status2 = U_ZERO_ERROR;		
 		Locale loc(locale);
@@ -446,7 +446,7 @@ public:
                 }
 	}
 
-	virtual long getOperationsPerIteration()
+	long getOperationsPerIteration() override
 	{
 		return num;
 	}
@@ -480,7 +480,7 @@ public:
         strcpy(locale, loc);
 	}
 
-	virtual void call(UErrorCode* /* status */)
+	void call(UErrorCode* /*status*/) override
 	{
 		UErrorCode status2 = U_ZERO_ERROR;		
 		Locale loc(locale);
@@ -493,7 +493,7 @@ public:
                 delete gen;
 	}
 
-	virtual long getOperationsPerIteration()
+	long getOperationsPerIteration() override
 	{
 		return num;
 	}
@@ -527,7 +527,7 @@ public:
         strcpy(locale, loc);
 	}
 
-	virtual void call(UErrorCode* /* status */)
+	void call(UErrorCode* /*status*/) override
 	{
 		UErrorCode status2 = U_ZERO_ERROR;		
 		Locale loc(locale);
@@ -541,7 +541,7 @@ public:
                 delete gen;
 	}
 
-	virtual long getOperationsPerIteration()
+	long getOperationsPerIteration() override
 	{
 		return num;
 	}
@@ -575,7 +575,7 @@ public:
         strcpy(locale, loc);
 	}
 
-	virtual void call(UErrorCode* status2)
+	void call(UErrorCode* status2) override
 	{
         Locale loc(locale);
         UErrorCode status = U_ZERO_ERROR;
@@ -657,7 +657,7 @@ public:
         }
     }
 
-	virtual long getOperationsPerIteration()
+	long getOperationsPerIteration() override
 	{
 		return num;
 	}
@@ -704,7 +704,7 @@ class StdioNumFmtFunction : public UPerfFunction
       strcpy(locale, loc);
     }
 
-  virtual void call(UErrorCode* status2)
+  void call(UErrorCode* status2) override
   {
     Locale loc(locale);
     UErrorCode status = U_ZERO_ERROR;
@@ -737,7 +737,7 @@ class StdioNumFmtFunction : public UPerfFunction
     }
   }
  
-  virtual long getOperationsPerIteration()
+  long getOperationsPerIteration() override
   {
     return num;
   }
@@ -783,7 +783,7 @@ public:
 		init();
 	}
 
-	virtual void call(UErrorCode* status2)
+	void call(UErrorCode* status2) override
 	{
         uint32_t listSize = UPRV_LENGTHOF(collation_strings_escaped);
         UErrorCode status = U_ZERO_ERROR; 
@@ -803,7 +803,7 @@ public:
         delete coll; 
     }
 
-	virtual long getOperationsPerIteration()
+	long getOperationsPerIteration() override
 	{
 		return num;
 	}
@@ -817,7 +817,7 @@ public:
 
 	DateFormatPerfTest(int32_t argc, const char* argv[], UErrorCode& status);
 	~DateFormatPerfTest();
-	virtual UPerfFunction* runIndexedTest(int32_t index, UBool exec,const char* &name, char* par);
+	UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char*& name, char* par) override;
 
 	UPerfFunction* DateFmt250();
 	UPerfFunction* DateFmt10000();
diff --git a/icu4c/source/test/perf/charperf/charperf.h b/icu4c/source/test/perf/charperf/charperf.h
index d9d652a7a09..b0654dae126 100644
--- a/icu4c/source/test/perf/charperf/charperf.h
+++ b/icu4c/source/test/perf/charperf/charperf.h
@@ -26,14 +26,14 @@ typedef void (*StdLibCharPerfFn)(wchar_t ch);
 class CharPerfFunction : public UPerfFunction
 {
 public:
-    virtual void call(UErrorCode* status)
+    void call(UErrorCode* status) override
     {
         for (UChar32 i = MIN_; i < MAX_; i ++) {
             (*m_fn_)(i);
         }
     }
 
-    virtual long getOperationsPerIteration()
+    long getOperationsPerIteration() override
     {
         return MAX_ - MIN_;
     }
@@ -53,7 +53,7 @@ private:
 class StdLibCharPerfFunction : public UPerfFunction
 {
 public:
-    virtual void call(UErrorCode* status)
+    void call(UErrorCode* status) override
     {
         // note wchar_t is unsigned, it will revert to 0 once it reaches 
         // 65535
@@ -62,7 +62,7 @@ public:
         }
     }
 
-    virtual long getOperationsPerIteration()
+    long getOperationsPerIteration() override
     {
         return MAX_ - MIN_;
     }
@@ -89,9 +89,9 @@ class CharPerformanceTest : public UPerfTest
 public:
     CharPerformanceTest(int32_t argc, const char *argv[], UErrorCode &status);
     ~CharPerformanceTest();
-    virtual UPerfFunction* runIndexedTest(int32_t index, UBool exec,
-        const char *&name, 
-        char *par = nullptr);
+    UPerfFunction* runIndexedTest(int32_t index, UBool exec,
+        const char*& name,
+        char* par = nullptr) override;
     UPerfFunction* TestIsAlpha();
     UPerfFunction* TestIsUpper();
     UPerfFunction* TestIsLower();
diff --git a/icu4c/source/test/perf/collperf/collperf.cpp b/icu4c/source/test/perf/collperf/collperf.cpp
index cceb58dd967..e9cb217cebb 100644
--- a/icu4c/source/test/perf/collperf/collperf.cpp
+++ b/icu4c/source/test/perf/collperf/collperf.cpp
@@ -102,9 +102,9 @@ public:
     CmdKeyGen(UErrorCode, UCollator * col,DWORD win_langid, int32_t count, DataIndex * data,Func fn,int32_t)
         :col(col),win_langid(win_langid), count(count), data(data), fn(fn){}
 
-        virtual long getOperationsPerIteration(){return count;}
+        long getOperationsPerIteration() override { return count; }
 
-        virtual void call(UErrorCode* status){
+        void call(UErrorCode* status) override {
             for(int32_t i = 0; i< count; i++){
                 (this->*fn)(i);
             }
@@ -155,9 +155,9 @@ public:
             ucol_closeElements(iter);
         }
 
-        virtual long getOperationsPerIteration(){return exec_count ? exec_count : 1;}
+        long getOperationsPerIteration() override { return exec_count ? exec_count : 1; }
 
-        virtual void call(UErrorCode* status){
+        void call(UErrorCode* status) override {
             exec_count = 0;
             for(int32_t i = 0; i< count; i++){
                 (this->*fn)(status, i);
@@ -215,9 +215,9 @@ public:
             fn = &CmdIterAll::icu_backward_all;
         }
     }
-    virtual long getOperationsPerIteration(){return exec_count ? exec_count : 1;}
+    long getOperationsPerIteration() override { return exec_count ? exec_count : 1; }
 
-    virtual void call(UErrorCode* status){
+    void call(UErrorCode* status) override {
         (this->*fn)(status);
     }
 
@@ -379,18 +379,18 @@ public:
             return utimer_getDeltaSeconds(&start,&stop); // ms
         }
 
-        virtual void call(UErrorCode* status){
+        void call(UErrorCode* status) override {
             exec_count = 0;
             memcpy(base, backup, num * width);
             qsort(base, num, width, fn);
         }
-        virtual double time(int32_t n, UErrorCode* status) {
+        double time(int32_t n, UErrorCode* status) override {
             double t1 = time_empty(n,status);
             double t2 = UPerfFunction::time(n, status);
             return  t2-t1;// < 0 ? t2 : t2-t1;
         }
 
-        virtual long getOperationsPerIteration(){ return exec_count?exec_count:1;}
+        long getOperationsPerIteration() override { return exec_count ? exec_count : 1; }
 };
 int32_t CmdQsort::exec_count;
 
@@ -411,13 +411,13 @@ public:
         :col(col),win_langid(win_langid), count(count), rnd(rnd), ord(ord), fn(fn),exec_count(0){}
 
 
-        virtual void call(UErrorCode* status){
+        void call(UErrorCode* status) override {
             exec_count = 0;
             for(int32_t i = 0; i< count; i++){ // search all data
                 binary_search(i);
             }
         }
-        virtual long getOperationsPerIteration(){ return exec_count?exec_count:1;}
+        long getOperationsPerIteration() override { return exec_count ? exec_count : 1; }
 
         void binary_search(int32_t random)	{
             int low   = 0;
@@ -684,7 +684,7 @@ public:
     temp++\
 
 
-    virtual UPerfFunction* runIndexedTest( /*[in]*/int32_t index, /*[in]*/UBool exec, /*[out]*/const char* &name, /*[in]*/ char* par = nullptr ){
+    UPerfFunction* runIndexedTest(/*[in]*/int32_t index, /*[in]*/UBool exec, /*[out]*/const char*& name, /*[in]*/char* par = nullptr) override {
         int temp = 0;
 
 #define TEST_KEYGEN(testname, func)\
diff --git a/icu4c/source/test/perf/collperf2/collperf2.cpp b/icu4c/source/test/perf/collperf2/collperf2.cpp
index e0a367189f8..9f9d95a4892 100644
--- a/icu4c/source/test/perf/collperf2/collperf2.cpp
+++ b/icu4c/source/test/perf/collperf2/collperf2.cpp
@@ -60,8 +60,8 @@ class Strcoll : public UPerfFunction
 public:
     Strcoll(const UCollator* coll, const CA_uchar* source, UBool useLen);
     ~Strcoll();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
 
 private:
     const UCollator *coll;
@@ -120,8 +120,8 @@ class Strcoll_2 : public UPerfFunction
 public:
     Strcoll_2(const UCollator* coll, const CA_uchar* source, const CA_uchar* target, UBool useLen);
     ~Strcoll_2();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
 
 private:
     const UCollator *coll;
@@ -172,8 +172,8 @@ class StrcollUTF8 : public UPerfFunction
 public:
     StrcollUTF8(const UCollator* coll, const CA_char* source, UBool useLen);
     ~StrcollUTF8();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
 
 private:
     const UCollator *coll;
@@ -232,8 +232,8 @@ class StrcollUTF8_2 : public UPerfFunction
 public:
     StrcollUTF8_2(const UCollator* coll, const CA_char* source, const CA_char* target, UBool useLen);
     ~StrcollUTF8_2();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
 
 private:
     const UCollator *coll;
@@ -283,8 +283,8 @@ class GetSortKey : public UPerfFunction
 public:
     GetSortKey(const UCollator* coll, const CA_uchar* source, UBool useLen);
     ~GetSortKey();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
 
 private:
     const UCollator *coll;
@@ -337,9 +337,9 @@ class NextSortKeyPart : public UPerfFunction
 public:
     NextSortKeyPart(const UCollator* coll, const CA_uchar* source, int32_t bufSize, int32_t maxIteration = -1);
     ~NextSortKeyPart();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
-    virtual long getEventsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
+    long getEventsPerIteration() override;
 
 private:
     const UCollator *coll;
@@ -404,9 +404,9 @@ class NextSortKeyPartUTF8 : public UPerfFunction
 public:
     NextSortKeyPartUTF8(const UCollator* coll, const CA_char* source, int32_t bufSize, int32_t maxIteration = -1);
     ~NextSortKeyPartUTF8();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
-    virtual long getEventsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
+    long getEventsPerIteration() override;
 
 private:
     const UCollator *coll;
@@ -472,8 +472,8 @@ class CppCompare : public UPerfFunction
 public:
     CppCompare(const Collator* coll, const CA_uchar* source, UBool useLen);
     ~CppCompare();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
 
 private:
     const Collator *coll;
@@ -531,8 +531,8 @@ class CppCompare_2 : public UPerfFunction
 public:
     CppCompare_2(const Collator* coll, const CA_uchar* source, const CA_uchar* target, UBool useLen);
     ~CppCompare_2();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
 
 private:
     const Collator *coll;
@@ -582,8 +582,8 @@ class CppCompareUTF8 : public UPerfFunction
 public:
     CppCompareUTF8(const Collator* coll, const CA_char* source, UBool useLen);
     ~CppCompareUTF8();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
 
 private:
     const Collator *coll;
@@ -652,8 +652,8 @@ class CppCompareUTF8_2 : public UPerfFunction
 public:
     CppCompareUTF8_2(const Collator* coll, const CA_char* source, const CA_char* target, UBool useLen);
     ~CppCompareUTF8_2();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
 
 private:
     const Collator *coll;
@@ -709,8 +709,8 @@ class CppGetCollationKey : public UPerfFunction
 public:
     CppGetCollationKey(const Collator* coll, const CA_uchar* source, UBool useLen);
     ~CppGetCollationKey();
-    virtual void call(UErrorCode* status);
-    virtual long getOperationsPerIteration();
+    void call(UErrorCode* status) override;
+    long getOperationsPerIteration() override;
 
 private:
     const Collator *coll;
@@ -772,7 +772,7 @@ public:
             : coll(coll), ucoll(ucoll), ops(0) {}
     virtual ~CollPerfFunction();
     /** Calls call() to set the ops field, and returns that. */
-    virtual long getOperationsPerIteration();
+    long getOperationsPerIteration() override;
 
 protected:
     const Collator& coll;
@@ -820,7 +820,7 @@ public:
             : UniStrCollPerfFunction(coll, ucoll, data16),
               dest(new UnicodeString*[d16->count]) {}
     virtual ~UniStrSort();
-    virtual void call(UErrorCode* status);
+    void call(UErrorCode* status) override;
 
 private:
     UnicodeString** dest;  // aliases only
@@ -910,7 +910,7 @@ public:
     StringPieceSortCpp(const Collator& coll, const UCollator *ucoll, const CA_char* data8)
             : StringPieceSort(coll, ucoll, data8) {}
     virtual ~StringPieceSortCpp();
-    virtual void call(UErrorCode* status);
+    void call(UErrorCode* status) override;
 };
 
 StringPieceSortCpp::~StringPieceSortCpp() {}
@@ -934,7 +934,7 @@ public:
     StringPieceSortC(const Collator& coll, const UCollator *ucoll, const CA_char* data8)
             : StringPieceSort(coll, ucoll, data8) {}
     virtual ~StringPieceSortC();
-    virtual void call(UErrorCode* status);
+    void call(UErrorCode* status) override;
 };
 
 StringPieceSortC::~StringPieceSortC() {}
@@ -958,7 +958,7 @@ public:
     UniStrBinSearch(const Collator& coll, const UCollator *ucoll, const CA_uchar* data16)
             : UniStrCollPerfFunction(coll, ucoll, data16) {}
     virtual ~UniStrBinSearch();
-    virtual void call(UErrorCode* status);
+    void call(UErrorCode* status) override;
 };
 
 UniStrBinSearch::~UniStrBinSearch() {}
@@ -994,7 +994,7 @@ public:
     StringPieceBinSearchCpp(const Collator& coll, const UCollator *ucoll, const CA_char* data8)
             : StringPieceBinSearch(coll, ucoll, data8) {}
     virtual ~StringPieceBinSearchCpp();
-    virtual void call(UErrorCode* status);
+    void call(UErrorCode* status) override;
 };
 
 StringPieceBinSearchCpp::~StringPieceBinSearchCpp() {}
@@ -1021,7 +1021,7 @@ public:
     StringPieceBinSearchC(const Collator& coll, const UCollator *ucoll, const CA_char* data8)
             : StringPieceBinSearch(coll, ucoll, data8) {}
     virtual ~StringPieceBinSearchC();
-    virtual void call(UErrorCode* status);
+    void call(UErrorCode* status) override;
 };
 
 StringPieceBinSearchC::~StringPieceBinSearchC() {}
@@ -1045,8 +1045,8 @@ class CollPerf2Test : public UPerfTest
 public:
     CollPerf2Test(int32_t argc, const char *argv[], UErrorCode &status);
     ~CollPerf2Test();
-    virtual UPerfFunction* runIndexedTest(
-        int32_t index, UBool exec, const char *&name, char *par = nullptr);
+    UPerfFunction* runIndexedTest(
+        int32_t index, UBool exec, const char*& name, char* par = nullptr) override;
 
 private:
     UCollator* coll;
diff --git a/icu4c/source/test/perf/dicttrieperf/dicttrieperf.cpp b/icu4c/source/test/perf/dicttrieperf/dicttrieperf.cpp
index 8fdfa76fc20..a880c79a54c 100644
--- a/icu4c/source/test/perf/dicttrieperf/dicttrieperf.cpp
+++ b/icu4c/source/test/perf/dicttrieperf/dicttrieperf.cpp
@@ -66,7 +66,7 @@ public:
         }
     }
 
-    virtual UPerfFunction *runIndexedTest(int32_t index, UBool exec, const char *&name, char *par=nullptr);
+    UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char*& name, char* par = nullptr) override;
 
     const char *getSourceDir() const { return sourceDir; }
 
@@ -99,7 +99,7 @@ public:
 
     // virtual void call(UErrorCode* pErrorCode) { ... }
 
-    virtual long getOperationsPerIteration() {
+    long getOperationsPerIteration() override {
         return pkg.getItemCount();
     }
 
@@ -159,7 +159,7 @@ public:
         delete[] toc;
     }
 
-    virtual void call(UErrorCode * /*pErrorCode*/) {
+    void call(UErrorCode* /*pErrorCode*/) override {
         int32_t count=pkg.getItemCount();
         const char *itemNameChars=itemNames.data();
         const char *name=itemNameChars;
@@ -249,7 +249,7 @@ public:
     PrefixBinarySearchPackageLookup(const DictionaryTriePerfTest &perf)
             : BinarySearchPackageLookup(perf) {}
 
-    virtual void call(UErrorCode * /*pErrorCode*/) {
+    void call(UErrorCode* /*pErrorCode*/) override {
         int32_t count=pkg.getItemCount();
         const char *itemNameChars=itemNames.data();
         const char *name=itemNameChars;
@@ -306,7 +306,7 @@ public:
         delete builder;
     }
 
-    virtual void call(UErrorCode *pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         int32_t count=pkg.getItemCount();
         const char *nameTrieBytes=builder->buildStringPiece(USTRINGTRIE_BUILD_SMALL, *pErrorCode).data();
         const char *name=itemNames.data();
@@ -331,7 +331,7 @@ class DictLookup : public UPerfFunction {
 public:
     DictLookup(const DictionaryTriePerfTest &perfTest) : perf(perfTest) {}
 
-    virtual long getOperationsPerIteration() {
+    long getOperationsPerIteration() override {
         return perf.numTextLines;
     }
 
@@ -439,7 +439,7 @@ public:
     UCharsTrieDictMatches(const DictionaryTriePerfTest &perfTest)
             : UCharsTrieDictLookup(perfTest) {}
 
-    virtual void call(UErrorCode *pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         UText text=UTEXT_INITIALIZER;
         int32_t lengths[20];
         const ULine *lines=perf.getCachedLines();
@@ -465,7 +465,7 @@ public:
     UCharsTrieDictContains(const DictionaryTriePerfTest &perfTest)
             : UCharsTrieDictLookup(perfTest) {}
 
-    virtual void call(UErrorCode * /*pErrorCode*/) {
+    void call(UErrorCode* /*pErrorCode*/) override {
         const ULine *lines=perf.getCachedLines();
         int32_t numLines=perf.getNumLines();
         for(int32_t i=0; i<numLines; ++i) {
@@ -585,7 +585,7 @@ public:
     BytesTrieDictMatches(const DictionaryTriePerfTest &perfTest)
             : BytesTrieDictLookup(perfTest) {}
 
-    virtual void call(UErrorCode *pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         if(noDict) {
             return;
         }
@@ -614,7 +614,7 @@ public:
     BytesTrieDictContains(const DictionaryTriePerfTest &perfTest)
             : BytesTrieDictLookup(perfTest) {}
 
-    virtual void call(UErrorCode * /*pErrorCode*/) {
+    void call(UErrorCode* /*pErrorCode*/) override {
         if(noDict) {
             return;
         }
diff --git a/icu4c/source/test/perf/howExpensiveIs/howExpensiveIs.cpp b/icu4c/source/test/perf/howExpensiveIs/howExpensiveIs.cpp
index 06e791e9f75..a8ab9f4a694 100644
--- a/icu4c/source/test/perf/howExpensiveIs/howExpensiveIs.cpp
+++ b/icu4c/source/test/perf/howExpensiveIs/howExpensiveIs.cpp
@@ -237,12 +237,12 @@ class SieveTest : public HowExpensiveTest {
 public:
   virtual ~SieveTest(){}
   SieveTest():HowExpensiveTest("SieveTest",__FILE__,__LINE__){}
-  virtual int32_t run(){return 0;} // dummy
-  int32_t runTest(double *subTime) {
+  int32_t run() override { return 0; } // dummy
+  int32_t runTest(double *subTime) override {
     *subTime = uprv_getSieveTime(nullptr);
     return U_LOTS_OF_TIMES;
   }
-  virtual int32_t runTests(double *subTime, double *marginOfError) {
+  int32_t runTests(double* subTime, double* marginOfError) override {
     *subTime = uprv_getSieveTime(marginOfError);
     return U_LOTS_OF_TIMES;
   }
@@ -256,8 +256,8 @@ public:
 #define OCStr(svc,ub,suffix,n) "Test_" # svc # ub # suffix # n
 #define OCRun(svc,ub,suffix) svc ## ub ## suffix
 // TODO: run away screaming
-#define OpenCloseTest(n, svc,suffix,c,a,d) class OCName(svc,_,Test_,suffix,n) : public HowExpensiveTest { public: OCName(svc,_,Test_,suffix,n)():HowExpensiveTest(OCStr(svc,_,suffix,n),__FILE__,__LINE__) c int32_t run() { int32_t i; for(i=0;i<U_LOTS_OF_TIMES;i++){ OCRun(svc,_,close) (  OCRun(svc,_,suffix) a );  } return i; }   void warmup() { OCRun(svc,_,close) ( OCRun(svc,_,suffix) a); } virtual ~ OCName(svc,_,Test_,suffix,n) () d };
-#define QuickTest(n,c,r,d)  class n : public HowExpensiveTest { public: n():HowExpensiveTest(#n,__FILE__,__LINE__) c int32_t run() r virtual ~n () d };
+#define OpenCloseTest(n, svc,suffix,c,a,d) class OCName(svc,_,Test_,suffix,n) : public HowExpensiveTest { public: OCName(svc,_,Test_,suffix,n)():HowExpensiveTest(OCStr(svc,_,suffix,n),__FILE__,__LINE__) c int32_t run() override { int32_t i; for(i=0;i<U_LOTS_OF_TIMES;i++){ OCRun(svc,_,close) (  OCRun(svc,_,suffix) a );  } return i; }   void warmup() override { OCRun(svc,_,close) ( OCRun(svc,_,suffix) a); } virtual ~ OCName(svc,_,Test_,suffix,n) () d };
+#define QuickTest(n,c,r,d)  class n : public HowExpensiveTest { public: n():HowExpensiveTest(#n,__FILE__,__LINE__) c int32_t run() override r virtual ~n () d };
 
 class NumTest : public HowExpensiveTest {
 private:
@@ -273,7 +273,7 @@ private:
   const char *fCStr;
   char name[100];
 public:
-  virtual const char *getName() {
+  const char* getName() override {
     if(name[0]==0) {
       sprintf(name,"%s:p=|%s|,str=|%s|",getClassName(),fCPat,fCStr);
     }
@@ -302,7 +302,7 @@ public:
   {
     name[0]=0;
   }
-  void warmup() {
+  void warmup() override {
     fFmt = initFmt();
     if(U_SUCCESS(setupStatus)) {
       double trial = unum_parseDouble(fFmt,fStr,fLen, nullptr, &setupStatus);
@@ -313,7 +313,7 @@ public:
       }
     }
   }
-  int32_t run() {
+  int32_t run() override {
     double trial=0.0;
     int i;
     for(i=0;i<U_LOTS_OF_TIMES;i++){
@@ -334,7 +334,7 @@ private:
   int32_t fAttrValue;
   char name2[100];
 protected:
-  virtual const char *getClassName() {
+  const char* getClassName() override {
     sprintf(name2,"AttrNumTest:%d=%d", fAttr,fAttrValue);
     return name2;
   }
@@ -345,7 +345,7 @@ public:
       fAttrValue(newValue)
   {
   }
-  virtual UNumberFormat* initFmt() {
+  UNumberFormat* initFmt() override {
     UNumberFormat *fmt = NumTest::initFmt();
     unum_setAttribute(fmt, fAttr,fAttrValue);
     return fmt;
@@ -362,7 +362,7 @@ private:
   int32_t fAttrValue;
   char name2[100];
 protected:
-  virtual const char *getClassName() {
+  const char* getClassName() override {
     sprintf(name2,"NOXNumTest:%d=%d", fAttr,fAttrValue);
     return name2;
   }
@@ -373,7 +373,7 @@ public:
       fAttrValue(newValue) */
   {
   }
-  virtual UNumberFormat* initFmt() {
+  UNumberFormat* initFmt() override {
     UNumberFormat *fmt = NumTest::initFmt();
     //unum_setAttribute(fmt, fAttr,fAttrValue);
     return fmt;
@@ -401,7 +401,7 @@ private:
   const char *fCStr;
   char name[100];
 public:
-  virtual const char *getName() {
+  const char* getName() override {
     if(name[0]==0) {
       sprintf(name,"%s:p=|%s|,str=|%s|",getClassName(),fCPat,fCStr);
     }
@@ -430,7 +430,7 @@ public:
   {
     name[0]=0;
   }
-  void warmup() {
+  void warmup() override {
     fFmt = initFmt();
     char16_t buf[100];
     if(U_SUCCESS(setupStatus)) {
@@ -447,7 +447,7 @@ public:
       }
     }
   }
-  int32_t run() {
+  int32_t run() override {
     int32_t trial;
     int i;
     char16_t buf[100];
@@ -486,7 +486,7 @@ private:
   const char *fCStr;
   char name[100];
 public:
-  virtual const char *getName() {
+  const char* getName() override {
     if(name[0]==0) {
       sprintf(name,"%s:p=|%s|,str=|%s|",getClassName(),fCPat,fCStr);
     }
@@ -554,7 +554,7 @@ public:
   {
     name[0]=0;
   }
-  void warmup() {
+  void warmup() override {
     fFmt = initFmt();
     char16_t buf[100];
     if(U_SUCCESS(setupStatus)) {
@@ -571,7 +571,7 @@ public:
       }
     }
   }
-  int32_t run() {
+  int32_t run() override {
     int32_t trial;
     int i;
     char16_t buf[100];
@@ -613,7 +613,7 @@ private:
   const char *fCStr;
   char name[100];
 public:
-  virtual const char *getName() {
+  const char* getName() override {
     if(name[0]==0) {
       sprintf(name,"%s:p=|%s|,str=|%s|,sp=|%s|",getClassName(),fCPat,fCStr, fExpect.data());
     }
@@ -645,7 +645,7 @@ public:
   {
     name[0]=0;
   }
-  void warmup() {
+  void warmup() override {
     fFmt = initFmt();
     UnicodeString buf;
     if(U_SUCCESS(setupStatus)) {
@@ -663,7 +663,7 @@ public:
     }
   }
 
-  int32_t run() {
+  int32_t run() override {
 #if U_DEBUG
     int32_t trial;
 #endif
diff --git a/icu4c/source/test/perf/leperf/PortableFontInstance.h b/icu4c/source/test/perf/leperf/PortableFontInstance.h
index 2f113cd0930..95ab0508b25 100644
--- a/icu4c/source/test/perf/leperf/PortableFontInstance.h
+++ b/icu4c/source/test/perf/leperf/PortableFontInstance.h
@@ -70,7 +70,7 @@ private:
 
 protected:
     const void *readFontTable(LETag tableTag) const { size_t ignored; return readFontTable(tableTag, ignored); }
-    const void *readFontTable(LETag tableTag, size_t &length) const;
+    const void *readFontTable(LETag tableTag, size_t &length) const override;
 
 public:
     PortableFontInstance(const char *fileName, float pointSize, LEErrorCode &status);
@@ -78,7 +78,7 @@ public:
     virtual ~PortableFontInstance();
 
     virtual const void *getFontTable(LETag tableTag) const;
-    virtual const void *getFontTable(LETag tableTag, size_t &length) const;
+    const void *getFontTable(LETag tableTag, size_t &length) const override;
 
     virtual const char *getNameString(le_uint16 nameID, le_uint16 platform, le_uint16 encoding, le_uint16 language) const;
 
@@ -88,39 +88,39 @@ public:
 
     virtual void deleteNameString(const LEUnicode16 *name) const;
 
-    virtual le_int32 getUnitsPerEM() const;
+    le_int32 getUnitsPerEM() const override;
 
     virtual le_uint32 getFontChecksum() const;
 
     virtual le_uint32 getRawChecksum() const;
 
-    virtual le_int32 getAscent() const;
+    le_int32 getAscent() const override;
 
-    virtual le_int32 getDescent() const;
+    le_int32 getDescent() const override;
 
-    virtual le_int32 getLeading() const;
+    le_int32 getLeading() const override;
 
     // We really want to inherit this method from the superclass, but some compilers
     // issue a warning if we don't implement it...
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper, le_bool filterZeroWidth) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper, le_bool filterZeroWidth) const override;
     
     // We really want to inherit this method from the superclass, but some compilers
     // issue a warning if we don't implement it...
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper) const override;
 
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch) const override;
 
-    virtual void getGlyphAdvance(LEGlyphID glyph, LEPoint &advance) const;
+    void getGlyphAdvance(LEGlyphID glyph, LEPoint &advance) const override;
 
-    virtual le_bool getGlyphPoint(LEGlyphID glyph, le_int32 pointNumber, LEPoint &point) const;
+    le_bool getGlyphPoint(LEGlyphID glyph, le_int32 pointNumber, LEPoint &point) const override;
 
-    float getXPixelsPerEm() const;
+    float getXPixelsPerEm() const override;
 
-    float getYPixelsPerEm() const;
+    float getYPixelsPerEm() const override;
 
-    float getScaleFactorX() const;
+    float getScaleFactorX() const override;
 
-    float getScaleFactorY() const;
+    float getScaleFactorY() const override;
 
 };
 
diff --git a/icu4c/source/test/perf/leperf/SimpleFontInstance.h b/icu4c/source/test/perf/leperf/SimpleFontInstance.h
index 14f5bfb48cb..7f91d41c174 100644
--- a/icu4c/source/test/perf/leperf/SimpleFontInstance.h
+++ b/icu4c/source/test/perf/leperf/SimpleFontInstance.h
@@ -40,37 +40,37 @@ public:
 
     virtual ~SimpleFontInstance();
 
-    virtual const void *getFontTable(LETag tableTag) const;
+    const void *getFontTable(LETag tableTag) const override;
 
-    virtual le_int32 getUnitsPerEM() const;
+    le_int32 getUnitsPerEM() const override;
 
-    virtual le_int32 getAscent() const;
+    le_int32 getAscent() const override;
 
-    virtual le_int32 getDescent() const;
+    le_int32 getDescent() const override;
 
-    virtual le_int32 getLeading() const;
+    le_int32 getLeading() const override;
 
     // We really want to inherit this method from the superclass, but some compilers
     // issue a warning if we don't implement it...
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper, le_bool filterZeroWidth) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper, le_bool filterZeroWidth) const override;
     
     // We really want to inherit this method from the superclass, but some compilers
     // issue a warning if we don't implement it...
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch, const LECharMapper *mapper) const override;
 
-    virtual LEGlyphID mapCharToGlyph(LEUnicode32 ch) const;
+    LEGlyphID mapCharToGlyph(LEUnicode32 ch) const override;
 
-    virtual void getGlyphAdvance(LEGlyphID glyph, LEPoint &advance) const;
+    void getGlyphAdvance(LEGlyphID glyph, LEPoint &advance) const override;
 
-    virtual le_bool getGlyphPoint(LEGlyphID glyph, le_int32 pointNumber, LEPoint &point) const;
+    le_bool getGlyphPoint(LEGlyphID glyph, le_int32 pointNumber, LEPoint &point) const override;
 
-    float getXPixelsPerEm() const;
+    float getXPixelsPerEm() const override;
 
-    float getYPixelsPerEm() const;
+    float getYPixelsPerEm() const override;
 
-    float getScaleFactorX() const;
+    float getScaleFactorX() const override;
 
-    float getScaleFactorY() const;
+    float getScaleFactorY() const override;
 
 };
 
diff --git a/icu4c/source/test/perf/leperf/cmaps.h b/icu4c/source/test/perf/leperf/cmaps.h
index a90057ffb5a..e8f9e946d00 100644
--- a/icu4c/source/test/perf/leperf/cmaps.h
+++ b/icu4c/source/test/perf/leperf/cmaps.h
@@ -44,7 +44,7 @@ public:
 
     virtual ~CMAPFormat4Mapper();
 
-    virtual LEGlyphID unicodeToGlyph(LEUnicode32 unicode32) const;
+    LEGlyphID unicodeToGlyph(LEUnicode32 unicode32) const override;
 
 protected:
     CMAPFormat4Mapper() {};
@@ -65,7 +65,7 @@ public:
 
     virtual ~CMAPGroupMapper();
 
-    virtual LEGlyphID unicodeToGlyph(LEUnicode32 unicode32) const;
+    LEGlyphID unicodeToGlyph(LEUnicode32 unicode32) const override;
 
 protected:
     CMAPGroupMapper() {};
diff --git a/icu4c/source/test/perf/localecanperf/localecanperf.cpp b/icu4c/source/test/perf/localecanperf/localecanperf.cpp
index 19fc99d5e25..1378aaf7a10 100644
--- a/icu4c/source/test/perf/localecanperf/localecanperf.cpp
+++ b/icu4c/source/test/perf/localecanperf/localecanperf.cpp
@@ -25,7 +25,7 @@ public:
         testCases.emplace_back("hy-SU");
     }
     ~LocaleCreateCanonical() {  }
-    virtual void call(UErrorCode* /* status */)
+    void call(UErrorCode* /*status*/) override
     {
         std::for_each(testCases.begin(), testCases.end(),
                       [](const std::string& s)
@@ -33,8 +33,8 @@ public:
                           Locale l = Locale::createCanonical(s.c_str());
                       });
     }
-    virtual long getOperationsPerIteration() { return testCases.size(); }
-    virtual long getEventsPerIteration() { return testCases.size(); }
+    long getOperationsPerIteration() override { return testCases.size(); }
+    long getEventsPerIteration() override { return testCases.size(); }
 private:
     std::vector<std::string> testCases;
 };
@@ -51,8 +51,8 @@ public:
     ~LocaleCanonicalizationPerfTest()
     {
     }
-    virtual UPerfFunction* runIndexedTest(
-        int32_t index, UBool exec, const char *&name, char *par = nullptr);
+    UPerfFunction* runIndexedTest(
+        int32_t index, UBool exec, const char*& name, char* par = nullptr) override;
 
 private:
     UPerfFunction* TestLocaleCreateCanonical()
diff --git a/icu4c/source/test/perf/normperf/dtfmtrtperf.h b/icu4c/source/test/perf/normperf/dtfmtrtperf.h
index 08a0af6317b..00e2f8362a0 100644
--- a/icu4c/source/test/perf/normperf/dtfmtrtperf.h
+++ b/icu4c/source/test/perf/normperf/dtfmtrtperf.h
@@ -66,7 +66,7 @@ public:
 		nLocales = locs;
 	}
 
-	virtual void call(UErrorCode* status)
+	void call(UErrorCode* status) override
 	{
         *status = U_ZERO_ERROR;
 
@@ -207,7 +207,7 @@ public:
 
 	}
 
-	virtual long getOperationsPerIteration()
+	long getOperationsPerIteration() override
 	{
 		return NUM_PATTERNS * nLocales * 6;
 	}
@@ -222,7 +222,7 @@ public:
 
 	DateTimeRoundTripPerfTest(int32_t argc, const char* argv[], UErrorCode& status);
 	~DateTimeRoundTripPerfTest();
-	virtual UPerfFunction* runIndexedTest(int32_t index, UBool exec,const char* &name, char* par);
+	UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char*& name, char* par) override;
 
 	UPerfFunction* RoundTripLocale1();
 	UPerfFunction* RoundTripLocale10();
diff --git a/icu4c/source/test/perf/normperf/normperf.h b/icu4c/source/test/perf/normperf/normperf.h
index 1ba042cbc8a..45f1a9abaed 100644
--- a/icu4c/source/test/perf/normperf/normperf.h
+++ b/icu4c/source/test/perf/normperf/normperf.h
@@ -46,7 +46,7 @@ private:
     int32_t options;
 
 public:
-    virtual void call(UErrorCode* status){
+    void call(UErrorCode* status) override {
         if(line_mode){
             if(uselen){
                 for(int32_t i = 0; i< numLines; i++){
@@ -67,7 +67,7 @@ public:
         }
 
     }
-    virtual long getOperationsPerIteration(){
+    long getOperationsPerIteration() override {
         if(line_mode){
             int32_t totalChars=0;
             for(int32_t i =0; i< numLines; i++){
@@ -117,7 +117,7 @@ private:
     int32_t options;
 
 public:
-    virtual void call(UErrorCode* status){
+    void call(UErrorCode* status) override {
         if(line_mode){
             if(uselen){
                 for(int32_t i = 0; i< numLines; i++){
@@ -136,7 +136,7 @@ public:
             }
         }
     }
-    virtual long getOperationsPerIteration(){
+    long getOperationsPerIteration() override {
         if(line_mode){
             int32_t totalChars=0;
             for(int32_t i =0; i< numLines; i++){
@@ -197,7 +197,7 @@ public:
 
     NormalizerPerformanceTest(int32_t argc, const char* argv[], UErrorCode& status);
     ~NormalizerPerformanceTest();
-    virtual UPerfFunction* runIndexedTest(int32_t index, UBool exec,const char* &name, char* par = nullptr);
+    UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char*& name, char* par = nullptr) override;
     /* NFC performance */
     UPerfFunction* TestICU_NFC_NFD_Text();
     UPerfFunction* TestICU_NFC_NFC_Text();
diff --git a/icu4c/source/test/perf/normperf/simplenormperf.cpp b/icu4c/source/test/perf/normperf/simplenormperf.cpp
index 8b2fbd48ce2..adff8eb1666 100644
--- a/icu4c/source/test/perf/normperf/simplenormperf.cpp
+++ b/icu4c/source/test/perf/normperf/simplenormperf.cpp
@@ -236,7 +236,7 @@ public:
     NormalizeUTF16(const Normalizer2 &n2, const UnicodeString &text) :
             norm2(n2), src(text), s(src.getBuffer()) {}
     virtual ~NormalizeUTF16();
-    virtual double call(int32_t iterations, int32_t pieceLength);
+    double call(int32_t iterations, int32_t pieceLength) override;
 
 private:
     const Normalizer2 &norm2;
@@ -269,7 +269,7 @@ public:
         s = src.data();
     }
     virtual ~NormalizeUTF8();
-    virtual double call(int32_t iterations, int32_t pieceLength);
+    double call(int32_t iterations, int32_t pieceLength) override;
 
 private:
     const Normalizer2 &norm2;
diff --git a/icu4c/source/test/perf/strsrchperf/strsrchperf.h b/icu4c/source/test/perf/strsrchperf/strsrchperf.h
index 3344c7cc012..008c7f4b6a2 100644
--- a/icu4c/source/test/perf/strsrchperf/strsrchperf.h
+++ b/icu4c/source/test/perf/strsrchperf/strsrchperf.h
@@ -28,11 +28,11 @@ private:
     UStringSearch* srch;
     
 public:
-    virtual void call(UErrorCode* status) {
+    void call(UErrorCode* status) override {
         (*fn)(srch, src, srcLen, pttrn, pttrnLen, status);
     }
     
-    virtual long getOperationsPerIteration() {
+    long getOperationsPerIteration() override {
         return (long) srcLen;
     }
     
@@ -57,7 +57,7 @@ private:
 public:
     StringSearchPerformanceTest(int32_t argc, const char *argv[], UErrorCode &status);
     ~StringSearchPerformanceTest();
-    virtual UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char *&name, char *par = nullptr);
+    UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char*& name, char* par = nullptr) override;
     UPerfFunction* Test_ICU_Forward_Search();
     UPerfFunction* Test_ICU_Backward_Search();
 };
diff --git a/icu4c/source/test/perf/ubrkperf/ubrkperf.h b/icu4c/source/test/perf/ubrkperf/ubrkperf.h
index 341f4cd285c..999769546d2 100644
--- a/icu4c/source/test/perf/ubrkperf/ubrkperf.h
+++ b/icu4c/source/test/perf/ubrkperf/ubrkperf.h
@@ -52,9 +52,9 @@ public:
   }
 
   ~ICUBreakFunction() {  delete m_brkIt_; }
-  virtual void call(UErrorCode *status) = 0;
-  virtual long getOperationsPerIteration() { return m_fileLen_; }
-  virtual long getEventsPerIteration() { return m_noBreaks_; }
+  void call(UErrorCode* status) override = 0;
+  long getOperationsPerIteration() override { return m_fileLen_; }
+  long getEventsPerIteration() override { return m_noBreaks_; }
   virtual UErrorCode getStatus() { return m_status_; }
 };
 
@@ -73,7 +73,7 @@ public:
       }
     }    
   }
-  virtual void call(UErrorCode *status) 
+  void call(UErrorCode* status) override
   {
     m_noBreaks_ = 0;
     int32_t j = 0;
@@ -97,7 +97,7 @@ public:
       m_noBreaks_++;
     }
   }
-  virtual void call(UErrorCode *status) 
+  void call(UErrorCode* status) override
   {
     m_noBreaks_ = 0;
     m_brkIt_->first();
@@ -109,7 +109,7 @@ public:
 
 class DarwinBreakFunction : public UPerfFunction {
 public:
-  virtual void call(UErrorCode *status) {};
+  void call(UErrorCode* status) override {};
 };
 
 class BreakIteratorPerformanceTest : public UPerfTest {
@@ -122,8 +122,8 @@ public:
   BreakIteratorPerformanceTest(int32_t argc, const char* argv[], UErrorCode& status);
   ~BreakIteratorPerformanceTest();
 
-  virtual UPerfFunction* runIndexedTest(int32_t index, UBool exec,
-    const char* &name, char* par = nullptr);
+  UPerfFunction* runIndexedTest(int32_t index, UBool exec,
+    const char*& name, char* par = nullptr) override;
 
   UPerfFunction* TestICUForward();
   UPerfFunction* TestICUIsBound();
diff --git a/icu4c/source/test/perf/unisetperf/draft/bitset.cpp b/icu4c/source/test/perf/unisetperf/draft/bitset.cpp
index 12c824ce841..49a3fd72745 100644
--- a/icu4c/source/test/perf/unisetperf/draft/bitset.cpp
+++ b/icu4c/source/test/perf/unisetperf/draft/bitset.cpp
@@ -188,7 +188,7 @@ public:
         delete restSet;
     }
 
-    UBool contains(UChar32 c) const {
+    UBool contains(UChar32 c) const override {
         if((uint32_t)c<=0xff) {
             return (UBool)((latin1Set[c>>5]&((uint32_t)1<<(c&0x1f)))!=0);
         } else if((uint32_t)c<0xffff) {
diff --git a/icu4c/source/test/perf/unisetperf/draft/trieset.cpp b/icu4c/source/test/perf/unisetperf/draft/trieset.cpp
index e05458cc46a..4e875136840 100644
--- a/icu4c/source/test/perf/unisetperf/draft/trieset.cpp
+++ b/icu4c/source/test/perf/unisetperf/draft/trieset.cpp
@@ -106,7 +106,7 @@ public:
         delete restSet;
     }
 
-    UBool contains(UChar32 c) const {
+    UBool contains(UChar32 c) const override {
         if((uint32_t)c<=0xff) {
             return (UBool)latin1[c];
         } else if((uint32_t)c<0xffff) {
diff --git a/icu4c/source/test/perf/unisetperf/unisetperf.cpp b/icu4c/source/test/perf/unisetperf/unisetperf.cpp
index 9310a06950f..99232e41e02 100644
--- a/icu4c/source/test/perf/unisetperf/unisetperf.cpp
+++ b/icu4c/source/test/perf/unisetperf/unisetperf.cpp
@@ -89,7 +89,7 @@ public:
         }
     }
 
-    virtual UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char* &name, char* par = nullptr);
+    UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char*& name, char* par = nullptr) override;
 
     // Count spans of characters that are in the set,
     // and spans of characters that are not in the set.
@@ -142,13 +142,13 @@ public:
 
     // virtual void call(UErrorCode* pErrorCode) { ... }
 
-    virtual long getOperationsPerIteration() {
+    long getOperationsPerIteration() override {
         // Number of code points tested:
         // Input code points, plus one for the end of each span except the last span.
         return testcase.countInputCodePoints+testcase.spanCount-1;
     }
 
-    virtual long getEventsPerIteration() {
+    long getEventsPerIteration() override {
         return testcase.spanCount;
     }
 
@@ -175,7 +175,7 @@ public:
     static UPerfFunction* get(const UnicodeSetPerformanceTest &testcase) {
         return new Contains(testcase);
     }
-    virtual void call(UErrorCode* pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         const UnicodeSet &set=testcase.set;
         const char16_t *s=testcase.getBuffer();
         int32_t length=testcase.getBufferLen();
@@ -237,7 +237,7 @@ public:
     static UPerfFunction* get(const UnicodeSetPerformanceTest &testcase) {
         return new SpanUTF16(testcase);
     }
-    virtual void call(UErrorCode* pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         const UnicodeSet &set=testcase.set;
         const char16_t *s=testcase.getBuffer();
         int32_t length=testcase.getBufferLen();
@@ -288,7 +288,7 @@ public:
     static UPerfFunction* get(const UnicodeSetPerformanceTest &testcase) {
         return new SpanBackUTF16(testcase);
     }
-    virtual void call(UErrorCode* pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         const UnicodeSet &set=testcase.set;
         const char16_t *s=testcase.getBuffer();
         int32_t length=testcase.getBufferLen();
@@ -338,7 +338,7 @@ public:
     static UPerfFunction* get(const UnicodeSetPerformanceTest &testcase) {
         return new SpanUTF8(testcase);
     }
-    virtual void call(UErrorCode* pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         const UnicodeSet &set=testcase.set;
         const char *s=testcase.utf8;
         int32_t length=testcase.utf8Length;
@@ -384,7 +384,7 @@ public:
     static UPerfFunction* get(const UnicodeSetPerformanceTest &testcase) {
         return new SpanBackUTF8(testcase);
     }
-    virtual void call(UErrorCode* pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         const UnicodeSet &set=testcase.set;
         const char *s=testcase.utf8;
         int32_t length=testcase.utf8Length;
diff --git a/icu4c/source/test/perf/usetperf/usetperf.cpp b/icu4c/source/test/perf/usetperf/usetperf.cpp
index 6bceab9e006..a2227b77d8d 100644
--- a/icu4c/source/test/perf/usetperf/usetperf.cpp
+++ b/icu4c/source/test/perf/usetperf/usetperf.cpp
@@ -36,10 +36,10 @@ private:
 public:
     CmdPattern(const char * pattern):pat(pattern,""){
     }
-    virtual long getOperationsPerIteration(){
+    long getOperationsPerIteration() override {
         return 1;
     }
-    virtual void call(UErrorCode* pErrorCode){
+    void call(UErrorCode* pErrorCode) override {
         set.applyPattern(pat, *pErrorCode);
     }
 };
@@ -61,11 +61,11 @@ public:
             }
         }
     }
-    virtual long getOperationsPerIteration(){
+    long getOperationsPerIteration() override {
         return total;
     }
 
-    virtual void call(UErrorCode* pErrorCode){
+    void call(UErrorCode* pErrorCode) override {
         (this->*op)();
     }
     void add(){
@@ -101,7 +101,7 @@ public:
     UsetPerformanceTest(int32_t argc, const char *argv[], UErrorCode &status) :UPerfTest(argc,argv,status){
     }
 
-    virtual UPerfFunction* runIndexedTest( int32_t index, UBool exec, const char* &name, char* par = nullptr ){
+    UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char*& name, char* par = nullptr) override {
         switch (index) {
             case 0: name = "titlecase_letter_add"; 
                 if (exec) return new CmdOp(U_TITLECASE_LETTER, &CmdOp::add) ; break;
diff --git a/icu4c/source/test/perf/ustrperf/stringperf.h b/icu4c/source/test/perf/ustrperf/stringperf.h
index b846ddf128c..d1d6c3b9661 100644
--- a/icu4c/source/test/perf/ustrperf/stringperf.h
+++ b/icu4c/source/test/perf/ustrperf/stringperf.h
@@ -68,7 +68,7 @@ class StringPerfFunction : public UPerfFunction
 {
 public:
 
-    virtual long getEventsPerIteration(){
+    long getEventsPerIteration() override {
         int loops = LOOPS;
         delete catICU;
         delete catStd;
@@ -90,7 +90,7 @@ public:
         return -1;
     }
 
-    virtual void call(UErrorCode* status)
+    void call(UErrorCode* status) override
     {
         if(line_mode_==true){
             if(uselen_){
@@ -127,7 +127,7 @@ public:
         }
     }
 
-    virtual long getOperationsPerIteration()
+    long getOperationsPerIteration() override
     {
         if(line_mode_==true){
             return numLines_;
@@ -350,9 +350,9 @@ class StringPerformanceTest : public UPerfTest
 public:
     StringPerformanceTest(int32_t argc, const char *argv[], UErrorCode &status);
     ~StringPerformanceTest();
-    virtual UPerfFunction* runIndexedTest(int32_t index, UBool exec,
-                                          const char *&name,
-                                          char *par = nullptr);
+    UPerfFunction* runIndexedTest(int32_t index, UBool exec,
+                                  const char*& name,
+                                  char* par = nullptr) override;
     UPerfFunction* TestCtor();
     UPerfFunction* TestCtor1();
     UPerfFunction* TestCtor2();
diff --git a/icu4c/source/test/perf/utfperf/utfperf.cpp b/icu4c/source/test/perf/utfperf/utfperf.cpp
index 706f2c9655a..4ad218cccc4 100644
--- a/icu4c/source/test/perf/utfperf/utfperf.cpp
+++ b/icu4c/source/test/perf/utfperf/utfperf.cpp
@@ -93,7 +93,7 @@ public:
         }
     }
 
-    virtual UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char* &name, char* par = nullptr);
+    UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char*& name, char* par = nullptr) override;
 
     const char16_t *getBuffer() const { return buffer; }
     int32_t getBufferLen() const { return bufferLen; }
@@ -139,7 +139,7 @@ public:
         }
     }
     // virtual void call(UErrorCode* pErrorCode) { ... }
-    virtual long getOperationsPerIteration(){
+    long getOperationsPerIteration() override {
         return countInputCodePoints;
     }
 
@@ -164,7 +164,7 @@ public:
             return nullptr;
         }
     }
-    virtual void call(UErrorCode* pErrorCode){
+    void call(UErrorCode* pErrorCode) override {
         const char16_t *pIn, *pInLimit;
         char16_t *pOut, *pOutLimit;
         char *pInter, *pInterLimit;
@@ -231,7 +231,7 @@ public:
             return nullptr;
         }
     }
-    virtual void call(UErrorCode* pErrorCode){
+    void call(UErrorCode* pErrorCode) override {
         const char16_t *pIn, *pInLimit;
         char *pInter, *pInterLimit;
 
@@ -284,7 +284,7 @@ public:
     ~FromUTF8() {
         ucnv_close(utf8Cnv);
     }
-    virtual void call(UErrorCode* pErrorCode){
+    void call(UErrorCode* pErrorCode) override {
         const char *pIn, *pInLimit;
         char *pInter, *pInterLimit;
         char16_t *pivotSource, *pivotTarget, *pivotLimit;
diff --git a/icu4c/source/test/perf/utrie2perf/utrie2perf.cpp b/icu4c/source/test/perf/utrie2perf/utrie2perf.cpp
index 5cbef68ad12..32ae5301268 100644
--- a/icu4c/source/test/perf/utrie2perf/utrie2perf.cpp
+++ b/icu4c/source/test/perf/utrie2perf/utrie2perf.cpp
@@ -81,7 +81,7 @@ public:
         }
     }
 
-    virtual UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char* &name, char* par = nullptr);
+    UPerfFunction* runIndexedTest(int32_t index, UBool exec, const char*& name, char* par = nullptr) override;
 
     const char16_t *getBuffer() const { return buffer; }
     int32_t getBufferLen() const { return bufferLen; }
@@ -103,7 +103,7 @@ public:
 
     // virtual void call(UErrorCode* pErrorCode) { ... }
 
-    virtual long getOperationsPerIteration() {
+    long getOperationsPerIteration() override {
         // Number of code points tested.
         return testcase.countInputCodePoints;
     }
@@ -121,7 +121,7 @@ public:
     static UPerfFunction* get(const UTrie2PerfTest &testcase) {
         return new CheckFCD(testcase);
     }
-    virtual void call(UErrorCode* pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         UErrorCode errorCode=U_ZERO_ERROR;
         qcResult=unorm_quickCheck(testcase.getBuffer(), testcase.getBufferLen(),
                                   UNORM_FCD, &errorCode);
@@ -189,7 +189,7 @@ public:
     static UPerfFunction* get(const UTrie2PerfTest &testcase) {
         return new ToNFC(testcase);
     }
-    virtual void call(UErrorCode* pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         UErrorCode errorCode=U_ZERO_ERROR;
         int32_t destLength=unorm_normalize(testcase.getBuffer(), testcase.getBufferLen(),
                                            UNORM_NFC, 0,
@@ -213,7 +213,7 @@ public:
     static UPerfFunction* get(const UTrie2PerfTest &testcase) {
         return new GetBiDiClass(testcase);
     }
-    virtual void call(UErrorCode* pErrorCode) {
+    void call(UErrorCode* pErrorCode) override {
         const char16_t *buffer=testcase.getBuffer();
         int32_t length=testcase.getBufferLen();
         UChar32 c;