java关于Integer设置-128到127的静态缓存

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今天在一个java群里，看到有个群友问到如下为什么第一个为true，第二个为false。

　　System.out.println(Integer.valueOf("50")==Integer.valueOf("50"));　　　//true
　　System.out.println(Integer.valueOf("200")==Integer.valueOf("200"));　　//false

由于一开始他问的第二句，我还想当然的以为是new的对象，肯定不一样，但是为什么第一句为true呢，后来通过查找资料发现

1、https://www.zhihu.com/question/29879295/answer/102396251

2、http://blog.csdn.net/chengzhezhijian/article/details/9628251

    /**

     * Returns a <tt>Integer</tt> instance representing the specified

     * <tt>int</tt> value.

     * If a new <tt>Integer</tt> instance is not required, this method

     * should generally be used in preference to the constructor

     * {@link #Integer(int)}, as this method is likely to yield

     * significantly better space and time performance by caching

     * frequently requested values.

     *

     * @param  i an <code>int</code> value.

     * @return a <tt>Integer</tt> instance representing <tt>i</tt>.

     * @since  1.5

     */

    public static Integer valueOf(int i) {

        if(i >= -128 && i <= IntegerCache.high)

            return IntegerCache.cache[i + 128];

        else

            return new Integer(i);

    }

 private static class IntegerCache {

        static final int high;

        static final Integer cache[];

        static {

            final int low = -128;

            // high value may be configured by property

            int h = 127;

            if (integerCacheHighPropValue != null) {

                // Use Long.decode here to avoid invoking methods that

                // require Integer's autoboxing cache to be initialized

                int i = Long.decode(integerCacheHighPropValue).intValue();

                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() {}

    }