Integer IntegerCache源码

/*public static void main(String[] args) {
        Integer a = 128, b = 128;
        Integer c = 127, d = 127;

        System.out.println(a == b);//false
        System.out.println(c == d);//true

    }*/
    
    
    
    /*public static void main(String[] args) {
        Integer int1 = Integer.valueOf("100");
        Integer int2 = Integer.valueOf("100");
        System.out.println(int1 == int2);//true
    }*/
    
    
    public static void main(String[] args) {
        Integer int1 = Integer.valueOf("300");
        Integer int2 = Integer.valueOf("300");
        System.out.println(int1 == int2);//false
    }
    

public static Integer valueOf(String s) throws NumberFormatException {
        return Integer.valueOf(parseInt(s, 10));
    }

public static Integer valueOf(int i) {
        if (i >= IntegerCache.low && i <= IntegerCache.high)
            return IntegerCache.cache[i + (-IntegerCache.low)];
        return new Integer(i);
    }

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) {
                try {
                    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);
                } 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++);

            // range [-128, 127] must be interned (JLS7 5.1.7)
            assert IntegerCache.high >= 127;
        }

        private IntegerCache() {}
    }