Integer ==与Equals【原创】

package Equals;

public class IntegerEquals {

    public static void main(String[] args) {
        printLine(128);
        Integer a=128;
        Integer b=128;
        System.out.println(a==b);
        System.out.println(a.equals(b));
        
        printLine(127);
        a=127;
        b=127;
        System.out.println(a==b);
        System.out.println(a.equals(b));
        
        printLine(-128);
        a=-128;
        b=-128;
        System.out.println(a==b);
        System.out.println(a.equals(b));
        
        printLine(-129);
        a=-129;
        b=-129;
        System.out.println(a==b);
        System.out.println(a.equals(b));
    }

    private static void printLine(int flag) {
        System.out.println("========"+flag+"========");
    }

}

Output:

========128========
false
true
========127========
true
true
========-128========
true
true
========-129========
false
true

原因：
基于减少对象创建次数和节省内存的考虑，[-128,127]之间的数字会被缓存。

[-128,127]这个范围取决于java.lang.Integer.IntegerCache.high参数的设置。

private static class IntegerCache {
    private IntegerCache(){}

    static final Integer cache[] = new Integer[-(-128) + 127 + 1];

    static {
        for(int i = 0; i < cache.length; i++)
        cache[i] = new Integer(i - 128);
    }
    }