Java Integer比较

代码

 1 @Slf4j
 2 public class IntegerCompare {
 3     public static void doCompare() {
 4 
 5         Integer a = 127; //Integer.valueOf(127)
 6         Integer b = 127; //Integer.valueOf(127)
 7         log.info("
Integer a = 127;
" +
 8                 "Integer b = 127;
" +
 9                 "a == b ? {}", a == b);    // true
10 
11         Integer c = 128; //Integer.valueOf(128)
12         Integer d = 128; //Integer.valueOf(128)
13         log.info("
Integer c = 128;
" +
14                 "Integer d = 128;
" +
15                 "c == d ? {}", c == d);   //false
16 
17         Integer e = 127; //Integer.valueOf(127)
18         Integer f = new Integer(127); //new instance
19         log.info("
Integer e = 127;
" +
20                 "Integer f = new Integer(127);
" +
21                 "e == f ? {}", e == f);   //false
22 
23         Integer g = new Integer(127); //new instance
24         Integer h = new Integer(127); //new instance
25         log.info("
Integer g = new Integer(127);
" +
26                 "Integer h = new Integer(127);
" +
27                 "g == h ? {}", g == h);  //false
28 
29         Integer i = 128; //unbox
30         int j = 128;
31         log.info("
Integer i = 128;
" +
32                 "int j = 128;
" +
33                 "i == j ? {}", i == j); //true
34     }
35 }

View Code

结果：

Integer a = 127;
Integer b = 127;
a == b ? true
2020-04-13 22:30:47.162  INFO 4492 --- [  restartedMain] com.example.newdemo.IntegerCompare       : 
Integer c = 128;
Integer d = 128;
c == d ? false
2020-04-13 22:30:47.162  INFO 4492 --- [  restartedMain] com.example.newdemo.IntegerCompare       : 
Integer e = 127;
Integer f = new Integer(127);
e == f ? false
2020-04-13 22:30:47.162  INFO 4492 --- [  restartedMain] com.example.newdemo.IntegerCompare       : 
Integer g = new Integer(127);
Integer h = new Integer(127);
g == h ? false
2020-04-13 22:30:47.162  INFO 4492 --- [  restartedMain] com.example.newdemo.IntegerCompare       : 
Integer i = 128;
int j = 128;
i == j ? true

结论：

=比较的是引用
equal比较的是integer实际的值

第一个相等，第二个不相等，是因为Interger.valueOf内部做了缓存（-127，127）。

a, b相同的引用。
c，d超过了缓存的范围直接new，产生不同的引用，所以不相等。

Integer e = 127;

Integer f = new Integer(127);

e从缓存中读取。f则是新的对象，用=判断时候是两个不同的引用，所以不相等。

Integer g = new Integer(127);
Integer h = new Integer(127);
g和h都是新的引用。

Integer i = 128;
int j = 128;
把装箱的 Integer 和基本类型 int 比较，前者会先拆箱再比较，比较的肯定是数值而不是引用，因此返回 true

Java Integer比较

结论：

=比较的是引用

equal比较的是integer实际的值