java Integer的值比较

    public static void main(String[] args) {        Integer a1 = 60;//直接赋数字是一个装箱过程,等同于Integer a1 = Integer.valueOf(60)        Integer a2 = new Integer(60);        Integer a3 = Integer.valueOf(60);        int a7 = 60;        Integer a4 = 128;//直接赋数字是一个装箱过程,等同于Integer a1 = Integer.valueOf(60)        Integer a5 = new Integer(128);        Integer a6 = Integer.valueOf(128);        int a8 = 128;        System.out.println("1:" + (a1 == a2));        System.out.println("2:" + (a1 == a3));        System.out.println("3:" + (a2 == a3));        System.out.println("4:" + (a1 == a7));        System.out.println("5:" + (a2 == a7));        System.out.println("6:" + (a4 == a5));        System.out.println("7:" + (a4 == a6));        System.out.println("8:" + (a5 == a6));        System.out.println("9:" + (a5 == a8));        System.out.println("10:" + (a6 == a8));        System.out.println("11:" + (a5.intValue() == a6.intValue()));        System.out.println("12:" + a5.equals(a6));    }//运行结果1:false2:true3:false4:true  引用类型Integer与值类型int比较比较的是值5:true6:false7:false8:false9:true10:true11:true12:true

java中Integer类型对应-128~127（jdk1.7之后，最大值可以设置，默认是127）之间的数是从缓冲区取的，所以用等号比较相等；但对于不在这区间的数字，是在堆中new出来的，地址空间不一样，也就不相等。

JDK1.6

public static Integer valueOf(int i) {    final int offset = 128;    if (i >= -128 && i <= 127) { // must cache         return IntegerCache.cache[i + offset];    }    return new Integer(i);}private static class IntegerCache {    private IntegerCache(){}    static final Integer cache[] = new Integer[-(-128) + 127 + 1];    static {        for(int i = 0; i < cache.length; i++)        cache[i] = new Integer(i - 128);    }}

JDK1.7

public static Integer valueOf(int i) {    assert IntegerCache.high >= 127;    if (i >= IntegerCache.low && i <= IntegerCache.high)        return IntegerCache.cache[i + (-IntegerCache.low)];    return new Integer(i);}//assert关键字表示断言1、assert <boolean表达式>如果<boolean表达式>为true，则程序继续执行。如果为false，则程序抛出AssertionError，并终止执行。2、assert <boolean表达式> : <错误信息表达式>如果<boolean表达式>为true，则程序继续执行。如果为false，则程序抛出java.lang.AssertionError，并输入<错误信息表达式>。 /** * 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 {    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) {            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);        }        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() {}}