????IntegerCache Class
????IntegerCache??Integer???ж???????private static???????????????????????塣
/**
* Cache to support the object identity semantics of autoboxing for values between
* -128 and 127 (inclusive) as required by JLS.
*
* The cache is initialized on first usage.  The size of the cache
* may be controlled by the {@code -XX:AutoBoxCacheMax=} option.
* During VM initialization?? java.lang.Integer.IntegerCache.high property
* may be set and saved in the private system properties in the
* sun.misc.VM class.
*/
private static class IntegerCache {
static final int low = -128;
static final int high;
static final Integer cache[];
static {
// high value may be configured by property
int h = 127;
String integerCacheHighPropValue =
sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
if (integerCacheHighPropValue != null) {
try {
int i = parseInt(integerCacheHighPropValue);
i = Math.max(i?? 127);
// Maximum array size is Integer.MAX_VALUE
h = Math.min(i?? Integer.MAX_VALUE - (-low) -1);
} catch( NumberFormatException nfe) {
// If the property cannot be parsed into an int?? ignore it.
}
}
high = h;
cache = new Integer[(high - low) + 1];
int j = low;
for(int k = 0; k < cache.length; k++)
cache[k] = new Integer(j++);
// range [-128?? 127] must be interned (JLS7 5.1.7)
assert IntegerCache.high >= 127;
}
private IntegerCache() {}
}
???????е?javadoc????????????????-128??127?????????????????127???????-XX:AutoBoxCacheMax=size???? ??????????for?????????????????????????????????洢??????????????С???????????Integer?????α?????????????????????????????????а?????????????????????????μ????(??????????????)??
??????????????????Java 5????????????Χ??????-128 ?? +127????????Java 6?У????????java.lang.Integer.IntegerCache.high???????????????????????ó????????????????????????????????????????????-128??127??Χ???????????Χ???????????????? ??????У?????????Integer?????????????????????????????????檔
????Java????淶?е???????
??????Boxing Conversion?????Java????淶(JLS)?漲???￡?
??????????????p??????
????-128??127????????(§3.10.1)
????true ?? false?????? (§3.10.3)
????‘u0000’?? ‘u007f’???????(§3.10.4)
???????????p?????a??b?????????????????????a==b?ж?a??b??????????
????????????????
????????????????????????Integer??????????????е??????????????????????????
??????ByteCache???????Byte????
??????ShortCache???????Short????
??????LongCache???????Long????
??????CharacterCache???????Character????
????Byte?? Short?? Long?й????Χ: -128 ?? 127??????Character?? ??Χ?? 0 ?? 127??????Integer?????????Χ????????