先看一个代码段：

public class csdn_Integer {
    public static void main(String[] args) {
        int a = 11;
        int b = 11;
        Integer c = 11;
        Integer d = 11;
        Integer e = new Integer(11);
        Integer f = 555;
        Integer g = 555;
        System.out.printf("a==b:%b\na==c:%b\nc==d:%b\nc==e:%b\ne==f:%b\n",a==b,a==c,c==d,c==e,f==g);
    }
}

结果 ：

a==b:true
a==c:true
c==d:true
c==e:false
e==f:false

Process finished with exit code 0

分析：

1.与String类似，Integer也有常量池，通过Integer = x；定义的变量会先在常量池查找（且Integer和int共享常量池），如果存在就引用，没有就在常量池新建；new Integer(x)；则不查找常量池，直接在堆中新建。

注意：这里Integer使用常量池的数据范围是-128 ~~ 127。超过这个范围的数据不引用常量，全部新建。

 

/**
 * 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
 * jdk.internal.misc.VM class.
 */

2.对于f与g，因为555 > 127所以无论怎么声明都是新建。