众所周知:java中Integer有一个常量池范围-128~127
Integer a = 500, b = 500;
System.out.println(a == b);//false
a = 100;
b = 100;
System.out.println(a == b);//true
相信也有一部分人在面试时,也被问到过这个问题,但是如果面试官继续追问:如果我想让
Integer a = 500, b = 500;
System.out.println(a == b);
也返回true,该怎么做?没准备的同学,可能会一时被问住,其实答案就在java.lang.Integer.IntegerCache 这个类的源码上
/**
* 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=<size>} 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 {
// ...
}
这个类的注释上,已经明细说明:
-XX:AutoBoxCacheMax=<size>
-Djava.lang.Integer.IntegerCache.high=<size>
这2个参数都可以控制上限。