在Java中取消装箱长 [英] Unboxing Long in java

问题描述

在某些代码中，我看到了这一点：

In some code I see this:

private void compute(Long a, Long b, Long c) {
        long result = a-(b+c);
...

结果存储在原语中似乎有点奇怪strong> long 而不是与其操作数对应的 Long 对象。

It seems a bit strange that the result is stored in a primitive long instead of a Long object corresponding to its operands.

是否有任何理由将结果存储为基元？

Are there any reason that a result should be stored as a primitive?

推荐答案

结果存储在原始long而不是与其操作数对应的Long对象中似乎有点奇怪。

It seems a bit strange that the result is stored in a primitive long instead of a Long object corresponding to its operands.

不，奇怪是你可以使用 + Long对象上的 - 运算符。在Java 5之前，这可能是语法错误。然后引入了自动装箱/拆箱。你在这段代码中看到的是 autounboxing ：运算符需要初始化，因此编译器会自动在对象上插入对 longValue（）的调用。然后对原始 long 值执行算术，结果也是 long ，无需进一步转换即可存储关于变量。

No, what is "strange" is that you can use the + and - operators on Long objects. Before Java 5, this would have been a syntax error. Then autoboxing/unboxing was introduced. What you're seeing in this code is autounboxing: the operators require primtives, so the compiler automatically inserts a call to longValue() on the objects. The arithmetic is then performed on primitive long values, and the result is also a long that can be stored without further conversion on the variable.

至于为什么代码执行此操作，真正的问题是为什么有人会使用 Long 键入而不是 long 。可能的原因：

As for why the code does this, the real question is why someone would use the Long type instead of long. Possible reasons:

• 这些值来自某些提供 Long 值的库/ API 。


• 这些值存储在集合中（ List ， Map ），不能保留原语。


• Sloppiness或货物崇拜节目 。


• 需要具有 null 值的能力，例如发出不可用或未初始化数据的信号。

• The values come from some library/API that delivers Long values.
• The values are stored in collections (List, Map), which cannot hold primitives.
• Sloppiness or cargo cult programming.
• The ability to have null values is required, e.g. to signal unavailable or uninitialized data.

请注意 Long 能否持有 null values表示计算（或更具体地说，编译器插入的 longValue（）调用）可能会因 NullPointerException - 代码应该以某种方式处理的可能性。

Note that the ability of Long to hold null values means that the calculation (or more specifically, the longValue() calls inserted by the compiler) can fail with a NullPointerException - a possibility the code should deal with somehow.

这篇关于在Java中取消装箱长的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！