关于Integer 为什么除了 -128到127。用==号比较返回false问题

电玩女神 2022-12-21 00:44 101阅读 0赞

Integer a = 128 等价于 Integer a = new Integer(128) // 自动装箱
    
    if (a == 128) 等价于 if (a.intValue() == 128) // 自动拆箱
    
    if (new Integer(128) == new Integer(128)) // false
    
    if (new Integer(127) == new Integer(127)) // ture 
    
    // -128 到 127 被Integer 静态内部类缓存
    
    Integer 内部类
        private static class IntegerCache {
            static final int low = -128;
            static final int high;
            // 缓存 -128 到 127常量数组
            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() {}
        }