package com.sitech.test;

/**

 * 自动装箱和拆箱 jdk1.6

 * @author liaowp

 *

 */

public class TestInteger {

    public static void main(String[] args) {

        Integer i1 = 80, i2 = 80, i3 = 999, i4 = 999;

        System.out.println(i1 == i2);//true

        System.out.println(i3 == i4);//false

    }

}

    /**

     * Returns an {@code Integer} instance representing the specified

     * {@code int} value.  If a new {@code Integer} 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.

     *

     * This method will always cache values in the range -128 to 127,

     * inclusive, and may cache other values outside of this range.

     *

     * @param  i an {@code int} value.

     * @return an {@code Integer} instance representing {@code i}.

     * @since  1.5

     */

    public static Integer valueOf(int i) {//是一个静态方法 IntegerCache是一个内部类

        assert IntegerCache.high >= 127;//断言  参考http://lavasoft.blog.51cto.com/62575/43735/

        if (i >= IntegerCache.low && i <= IntegerCache.high)//如果i大于对于IntegerCache.low()且i小于等于IntegerCache.high

            return IntegerCache.cache[i + (-IntegerCache.low)];//直接从缓存取出来

        return new Integer(i);//新创建一个Integer对象

    }

    /**

     * 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 -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 {//静态类哦

        static final int low = -128;//最小值是-128

        static final int high;//最高

        static final Integer cache[];//缓存数组  这三个都final，不可修改的

        static {//静态代码块   静态代码块会比改造方法先执行

            // high value may be configured by property

            int h = 127;//默认的

            String integerCacheHighPropValue =//定义一个String

                sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");//取得设置的值

            if (integerCacheHighPropValue != null) {//如果设置了就用设置的值

                int i = parseInt(integerCacheHighPropValue);//把String转换为int

                i = Math.max(i, 127);//获得i和127的更大的一个，其实是不能小与默认的

                // Maximum array size is Integer.MAX_VALUE

                h = Math.min(i, Integer.MAX_VALUE - (-low));//如果取的小的那个，不能超过Integer的最大值+low

            }

            high = h;//最大值为127

            cache = new Integer[(high - low) + 1];//创建缓存数组大小

            int j = low;//最小值

            for(int k = 0; k < cache.length; k++)

                cache[k] = new Integer(j++);//缓存初始化

        }

        private IntegerCache() {}//私有构造

    }