平等双方之间的差值/ equals和==操作符？ [英] Difference between Equals/equals and == operator?

问题描述

什么是 A == b 和 a.Equals之间的差值（B）？

推荐答案

假设类型的 A 和 B 是引用类型：

Assuming the types of a and b are reference types:

• 在Java中，==总是比较对的标识的 - 即两个值是否是同一个对象的引用。这也被称为的引用相等的。 Java没有任何用户定义的操作符重载。

• In Java, == will always compare for identity - i.e. whether the two values are references to the same object. This is also called reference equality. Java doesn't have any user-defined operator overloading.

在C＃这取决于。除非有一个操作符重载处理它，==会像Java的（即比较参考平等）。但是，如果有相匹配的过载的编译时间的类型 A 和 B （例如，如果他们都声明为字符串），那么超载将被调用。这可以表现怎么想，但通常实现的值相等的（即 A 和 B 可以参考，但不同的等于的价值观，它仍然会返回true）。

In C# it depends. Unless there's an overloaded operator which handles it, == will behave like Java (i.e. comparing for reference equality). However, if there's an overload which matches the compile-time types of a and b (e.g. if they're both declared as strings) then that overload will be called. That can behave how it wants, but it typically implements value equality (i.e. a and b can refer to different but equal values and it would still return true).

在两种语言中， a.Equals（B）或 a.equals（B）将调用虚拟等于 / 等于通过声明 Method对象，除非更具体超载已被的编译时类型介绍 A 。这可能会或可能不会在对象的执行时间类型覆盖的引用。在这两个.NET和Java中，对象执行还检查身份。请注意，这依赖于的执行时间型的而不是编译时类型的是重载依赖。

In both languages, a.Equals(b) or a.equals(b) will call the virtual Equals/equals method declared by Object, unless a more specific overload has been introduced by the compile-time type of a. This may or may not be overridden in the execution-time type of the object that a refers to. In both .NET and Java, the implementation in Object also checks for identity. Note that this depends on the execution-time type rather than the compilation-time type that overload resolution depends on.

当然，如果 A 是空，那么你会得到一个的NullReferenceException / NullPointerException异常当您尝试调用 a.equals（b）或 a.Equals（b）。

Of course, if a is null then you'll get a NullReferenceException/NullPointerException when you try to call a.equals(b) or a.Equals(b).

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