A==B vs B==A，有什么区别 [英] A==B vs B==A, What are the differences

问题描述

所以长话短说.一位教授在课堂上提出了这个问题作为讨论的开始.除了显而易见的

So to make a long story short. A professor asked this question in class as a discussion starter. Besides the obvious

B = new SomeClass("B"); // But B can be null, can can be new SomeClass("A");
A = new SomeClass("A");
A==B

比较时会保证没有NPE，使用B==A而不是A==B的原因是什么?

will guarantee no NPE when comparing, what are the reasons to use B==A instead of A==B?

其中 A 和 B 属于同一类型，这与语言无关.所以你可以假设 A.equals(B) 用于 Java，或者 C 或 C++ 等中的等效语法......

Where A and B are of same type, and this is language independent. So you can assume A.equals(B) for Java, or equivalent syntax in C or C++ etc....

不，这不是家庭作业.

推荐答案

在 Java 中，A == B 和 B == A 始终具有相同的语义.在 C#(具有运算符重载)中，如果 B 是 A 类的子类的实例，则可能会有所不同.

In Java, A == B and B == A always have the same semantics. In C# (which has operator overloading), there can be a difference if, say, B is an instance of a subclass of the class of A.

请注意，A.equals(B) 不等同于 A == B.

Note that A.equals(B) is not equivalent to A == B.

这篇关于A==B vs B==A，有什么区别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！