哪个更有效：if（null == variable）或if（variable == null）？ [英] Which is more effective: if (null == variable) or if (variable == null)?

问题描述

在Java中，哪个更有效，有什么区别？

In Java, which will be more effective, and what are the differences?

if (null == variable)

或

if (variable == null)

推荐答案

< sup>（与此问题类似： null == object and object =之间的差异= = null ）

我想说这两个表达式之间的性能完全没有区别。

I would say that there is absolutely no difference in performance between those two expressions.

有趣的是，编译后的字节码（由Suns javac发出）在两种情况下看起来有点不同。

Interestingly enough however, the compiled bytecode (as emitted by Suns javac) looks a bit different for the two cases.

对于 boolean b = variable == null ：

 3: aload_1               // load variable
 4: ifnonnull 11          // check if it's null
 7: iconst_1              // push 1
 8: goto 12           
11: iconst_0              // push 0
12: istore_2              // store

boolean b = null == variable ：

 3: aconst_null           // push null
 4: aload_1               // load variable
 5: if_acmpne 12          // check if equal
 8: iconst_1              // push 1
 9: goto 13
12: iconst_0              // push 0
13: istore_2              // store

正如@Bozho所说，变量== null 是最常见，默认和首选的样式。

As @Bozho says, variable == null is the most common, default and preferred style.

但在某些情况下，我倾向于设置 null 在前面。例如，在以下情况中：

For certain situations however, I tend to put the null in front. For instance in the following case:

String line;
while (null != (line = reader.readLine()))
    process(line);

这篇关于哪个更有效：if（null == variable）或if（variable == null）？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！