今天看了虚拟机的自动装箱部分,有一点很疑惑,我分别初始化了四个Integer对象,两两相等,其中两个值比较小,其中两个值稍大一点,然后判断它们是否相等,结果很出乎意料,一个相等,一个不相等。代码如下:
Integer t1 = Integer.valueOf(345);
Integer t2 = Integer.valueOf(345);
Integer t3 = Integer.valueOf(1);
Integer t4 = Integer.valueOf(1);
System.out.println(t1 == t2); // false
System.out.println(t3 == t4); // true
难道Java判定int类型是否相等还要看大小?我做了一个测试,发现小于128的输出为true,大于等于128的都输出为false,大佬们知道这是为什么嘛?
List<Integer> equalsValues = new ArrayList<>(100);
List<Integer> nEqualsValues = new ArrayList<>(100);
for(int i = 0; i < 200; i ++) {
Integer t1 = Integer.valueOf(i);
Integer t2 = Integer.valueOf(i);
if(t1 == t2) {
equalsValues.add(i);
} else {
nEqualsValues.add(i);
}
}
System.out.println("equalsValues:" + equalsValues);
System.out.println();
System.out.println("notEqualsValues:" + nEqualsValues);
输出结果是这样的:
equalsValues:[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127]
notEqualsValues:[128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199]