java基本类型对应包装类的静态缓存

阅读jdk源码，可以发现，对于基本类型的包装类，是有静态缓存。

1、对Boolean类型,true和false都有对应的缓存，源码为：

/** * The {@code Boolean} object corresponding to the primitive * value {@code true}. */public static final Boolean TRUE = new Boolean(true);/** * The {@code Boolean} object corresponding to the primitive * value {@code false}. */public static final Boolean FALSE = new Boolean(false);

2、对于Integer,范围在-128至127内的，都有对应的缓存，源码为：

/** * 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() {}}

3、对于Byte/Short/Long，是和Integer类似的，范围在-128至127内的，都有对应的缓存

总结，对于上述基本类型对应的包装类，只要在缓存范围内，即-128至127范围（一个字节，补码表示的范围）内，

我们是可以直接用=判断相相等的。

4、注意，对于Float和Double类型，并没有对应的缓存。