Integer a1 = 10, b1 = 128;
Integer a2 = 10, b2 = 128;
Integer a3 = new Integer(10);
Integer b3 = new Integer(128);
System.out.println(a1==a2);//true
System.out.println(a1==a3);//false
System.out.println(b1==b2);//false
System.out.println(b1==b3);//false

Integer a1 = = Integer.valueOf(10);

private static class IntegerCache {
//IntegerCache.low的值為-128,被final修飾表示必須賦值且賦值后便不可再次更改
    static final int low = -128;
    //high值雖也被final修飾但并未賦初值,意味著要在后面賦初值
    static final int high;
    //用來存儲(chǔ)緩存的Integer對(duì)象
    static final Integer cache[];
    static {
        int h = 127;
//從虛擬機(jī)配置中獲取配置"java.lang.Integer.IntegerCache.high"的值,可以自己修改虛擬機(jī)配置,默認(rèn)沒有該條配置
        String integerCacheHighPropValue =
       sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
        if (integerCacheHighPropValue != null) {
            try {
//將獲取的String配置值轉(zhuǎn)為int
                int i = parseInt(integerCacheHighPropValue);
                i = Math.max(i, 127);
//配置的值若超過int類型能表示的最大值,肯定是不行的,同時(shí)也是因?yàn)榫彺娴膶?duì)象都是存在了數(shù)組中而數(shù)組的大小也是有上線的,超過數(shù)組最大上限就緩存不下了
                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++);
        assert IntegerCache.high >= 127;
    }
    private IntegerCache() {}
}

Integer a1 = new Integer(100); 
int a2 = 100;
Integer a3 = new Integer(100);
//當(dāng)一個(gè)基本類型和一個(gè)包裝類型比較時(shí)，包裝類型會(huì)被自動(dòng)拆包進(jìn)行比較
System.out.println(a1 == a2);//true
//equals方法內(nèi)部調(diào)用了intValue方法,該方法會(huì)返回Integer對(duì)象中使用int修飾的value值,這個(gè)過程就是所謂的拆包
System.out.println(a1 == a3);//false
System.out.println(a1.equals(a3));//true