为什么某些Integer对象的== true? [英] Why is == true for some Integer objects?
问题描述
可能重复:
整数包装器对象仅在值127内共享相同的实例?
我从Khalid Mughal SCJP复制了以下程序片段,但我无法理解输出的
。
I have copied the following program snippet from the Khalid Mughal SCJP, but I am unable to
understand the output.
public class RQ200_60 {
public static void main(String[] args) {
Integer i = -10;
Integer j = -10;
System.out.print(i==j); // output: true -- why true?
System.out.print(i.equals(j)); // output: true
Integer n = 128;
Integer m = 128;
System.out.print(n==m); // output: false
System.out.print(n.equals(m)); // output: true
}
}
上述程序输出为true对于第一个print语句,但它应该给出false,因为它是与==关系运算符的引用比较。但第三次打印出现错误,我不明白这种不一致。
The above program giving output true for the first print statement but it supposed to give false because it is reference comparison with == relational operator. But third print gives false and I don't understand this inconsistency.
非常感谢解释!
推荐答案
在第一种情况下,对象 i
和 j
都指向相同的缓存对象。默认情况下,-128和127之间的范围缓存为 Integer
Object。我们可以使用 JVM参数
来增加范围
In the first case, both the objects i
and j
are pointing to the same cached object. By default, the range between -128 and 127 are cached as Integer
Object. We can increase the range using JVM arguments
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