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Implement fieldDifference (j438)

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X-SVN-Rev: 1620
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Alan Liu 2000-06-14 17:00:20 +00:00
parent 52e4b81862
commit c5d118a49f
2 changed files with 164 additions and 0 deletions
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82
icu4j/src/com/ibm/icu/util/Calendar.java
View file

@ -1271,6 +1271,88 @@ public abstract class Calendar implements Serializable, Cloneable {
}
}
/**
* [NEW]
* Return the difference between the given time and the time this
* calendar object is set to. If this calendar is set
* <em>before</em> the given time, the returned value will be
* positive. If this calendar is set <em>after</em> the given
* time, the returned value will be negative. The
* <code>field</code> parameter specifies the units of the return
* value. For example, if <code>fieldDifference(when,
* Calendar.MONTH)</code> returns 3, then this calendar is set to
* 3 months before <code>when</code>, and possibly some addition
* time less than one month.
*
* <p>As a side effect of this call, this calendar is advanced
* toward <code>when</code> by the given amount. That is, calling
* this method has the side effect of calling <code>add(field,
* n)</code>, where <code>n</code> is the return value.
*
* <p>Usage: To use this method, call it first with the largest
* field of interest, then with progressively smaller fields. For
* example:
*
* <pre>
* int y = cal.fieldDifference(when, Calendar.YEAR);
* int m = cal.fieldDifference(when, Calendar.MONTH);
* int d = cal.fieldDifference(when, Calendar.DATE);</pre>
*
* computes the difference between <code>cal</code> and
* <code>when</code> in years, months, and days.
*
* <p>Note: <code>fieldDifference()</code> is
* <em>asymmetrical</em>. That is, in the following code:
*
* <pre>
* cal.setTime(date1);
* int m1 = cal.fieldDifference(date2, Calendar.MONTH);
* int d1 = cal.fieldDifference(date2, Calendar.DATE);
* cal.setTime(date2);
* int m2 = cal.fieldDifference(date1, Calendar.MONTH);
* int d2 = cal.fieldDifference(date1, Calendar.DATE);</pre>
*
* one might expect that <code>m1 == -m2 && d1 == -d2</code>.
* However, this is not generally the case, because of
* irregularities in the underlying calendar system (e.g., the
* Gregorian calendar has a varying number of days per month).
*
* @param when the date to compare this calendar's time to
* @param field the field in which to compute the result
* @return the difference, either positive or negative, between
* this calendar's time and <code>when</code>, in terms of
* <code>field</code>.
*/
public int fieldDifference(Date when, int field) {
int result = 0;
long targetMs = when.getTime();
long ms = getTimeInMillis();
if (ms < targetMs) {
for (;;) {
add(field, 1);
long newMs = getTimeInMillis();
if (newMs > targetMs) {
setTimeInMillis(ms);
break;
}
ms = newMs;
++result;
}
} else if (ms > targetMs) {
for (;;) {
add(field, -1);
long newMs = getTimeInMillis();
if (newMs < targetMs) {
setTimeInMillis(ms);
break;
}
ms = newMs;
--result;
}
}
return result;
}
/**
* Sets the time zone with the given time zone value.
* @param value the given time zone.

82
icu4j/src/com/ibm/util/Calendar.java
View file

@ -1271,6 +1271,88 @@ public abstract class Calendar implements Serializable, Cloneable {
}
}
/**
* [NEW]
* Return the difference between the given time and the time this
* calendar object is set to. If this calendar is set
* <em>before</em> the given time, the returned value will be
* positive. If this calendar is set <em>after</em> the given
* time, the returned value will be negative. The
* <code>field</code> parameter specifies the units of the return
* value. For example, if <code>fieldDifference(when,
* Calendar.MONTH)</code> returns 3, then this calendar is set to
* 3 months before <code>when</code>, and possibly some addition
* time less than one month.
*
* <p>As a side effect of this call, this calendar is advanced
* toward <code>when</code> by the given amount. That is, calling
* this method has the side effect of calling <code>add(field,
* n)</code>, where <code>n</code> is the return value.
*
* <p>Usage: To use this method, call it first with the largest
* field of interest, then with progressively smaller fields. For
* example:
*
* <pre>
* int y = cal.fieldDifference(when, Calendar.YEAR);
* int m = cal.fieldDifference(when, Calendar.MONTH);
* int d = cal.fieldDifference(when, Calendar.DATE);</pre>
*
* computes the difference between <code>cal</code> and
* <code>when</code> in years, months, and days.
*
* <p>Note: <code>fieldDifference()</code> is
* <em>asymmetrical</em>. That is, in the following code:
*
* <pre>
* cal.setTime(date1);
* int m1 = cal.fieldDifference(date2, Calendar.MONTH);
* int d1 = cal.fieldDifference(date2, Calendar.DATE);
* cal.setTime(date2);
* int m2 = cal.fieldDifference(date1, Calendar.MONTH);
* int d2 = cal.fieldDifference(date1, Calendar.DATE);</pre>
*
* one might expect that <code>m1 == -m2 && d1 == -d2</code>.
* However, this is not generally the case, because of
* irregularities in the underlying calendar system (e.g., the
* Gregorian calendar has a varying number of days per month).
*
* @param when the date to compare this calendar's time to
* @param field the field in which to compute the result
* @return the difference, either positive or negative, between
* this calendar's time and <code>when</code>, in terms of
* <code>field</code>.
*/
public int fieldDifference(Date when, int field) {
int result = 0;
long targetMs = when.getTime();
long ms = getTimeInMillis();
if (ms < targetMs) {
for (;;) {
add(field, 1);
long newMs = getTimeInMillis();
if (newMs > targetMs) {
setTimeInMillis(ms);
break;
}
ms = newMs;
++result;
}
} else if (ms > targetMs) {
for (;;) {
add(field, -1);
long newMs = getTimeInMillis();
if (newMs < targetMs) {
setTimeInMillis(ms);
break;
}
ms = newMs;
--result;
}
}
return result;
}
/**
* Sets the time zone with the given time zone value.
* @param value the given time zone.