由自动装箱和拆箱引发我看Integer源码

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
}