为什么Java中2个Long变量与==运算符不相等？ [英] Why are 2 Long variables not equal with == operator in Java?

问题描述

当我尝试比较2个Long变量时，我遇到了一个非常奇怪的问题，它们始终显示为false，并且可以通过在Eclipse中进行调试来确保它们具有相同的数字值：

I got a very strange problem when I'm trying to compare 2 Long variables, they always show false and I can be sure they have the same number value by debugging in Eclipse:

if (user.getId() == admin.getId()) {
    return true; // Always enter here
} else {
    return false;
}

以上两个返回值都是对象类型Long，这使我感到困惑。并确认我编写了这样的主要方法：

Both of above 2 return values are object-type Long, which confused me. And to verify that I wrote a main method like this:

Long id1 = 123L;
Long id2 = 123L;

System.out.println(id1 == id2);

它显示为真。

所以可以有人给我想法吗？我从事Java开发已经3年了，但是无法解释这种情况。

So can somebody give me ideas?. I've been working in Java Development for 3 years but cannot explain this case.

推荐答案

== 比较引用。 equals（）比较值。这两个Long是对象，因此使用 == 运算符时会比较对象引用。

== compares references, .equals() compares values. These two Longs are objects, therefore object references are compared when using == operator.

但是，请注意 Long id1 = 123L; 文字值 123L 将自动装箱为 Long 对象使用 Long.valueOf（String），并且在内部，此过程将使用LongCache，该LongCache具有 [-128,127] 范围，而123在此范围内，这意味着将缓存长对象，而这两个实际上是相同的对象。

However, note that in Long id1 = 123L; literal value 123L will be auto-boxed into a Long object using Long.valueOf(String), and internally, this process will use a LongCache which has a [-128,127] range, and 123 is in this range, which means, that the long object is cached, and these two are actually the same objects.

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