Integer使用双等号比较会发生什么

话很少说，根据如下程序运行，打印的结果为何不一样?

Integer a = 100;
Integer b = 100;

System.out.println(a == b);//print : true


Integer a = 200;
Integer b = 200;

System.out.println(a == b);//print : false

以上两段代码在执行后为何会出现这样神奇的效果，纠察缘由在Integer的源码中一段特殊的代码，在代码中会在虚拟机加载时将-128至127的数据提早缓存到内存中，因此会致使双等号比较会出现不一致的问题（内存引用地址已缓存）。

在开发中对象类型的比较必定记得使用eques进行内容比较。

/**
     * 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 {
        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() {}
    }