Integer 中的缓存类IntegerCache

Cache为[-128,127],IntegerCache有一个静态的Integer数组，在类加载时就将-128 到 127 的Integer对象创建了，并保存在cache数组中，一旦程序调用valueOf 方法，如果取的值是在-128 到 127 之间就直接在cache缓存数组中去取Integer对象，超出范围就new一个对象。

 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) {
                int i = parseInt(integerCacheHighPropValue);
                i = Math.max(i, 127);
                // Maximum array size is Integer.MAX_VALUE
                h = Math.min(i, Integer.MAX_VALUE - (-low));
            }
            high = h;

            cache = new Integer[(high - low) + 1];
            int j = low;
            for(int k = 0; k < cache.length; k++)
                cache[k] = new Integer(j++);
        }

        private IntegerCache() {}
    }

                Integer i = 127;
		Integer j = 127;
		System.out.println(i==j);//true
		Integer i1 = 128;
		Integer j1 = 128;
		System.out.println(i1==j1);//false
		Integer i2 = new Integer(127);
		Integer j2= new Integer(127);
		System.out.println(i2==j2);//false
		System.out.println(200 == i); //false