等于/等于和 == 运算符之间的区别? [英] Difference between Equals/equals and == operator?

问题描述

a == b 和 a.Equals(b) 有什么区别?

推荐答案

假设 a 和 b 的类型是引用类型:

Assuming the types of a and b are reference types:

• 在 Java 中，== 将始终比较 identity - 即两个值是否是对同一对象的引用.这也称为引用相等.Java 没有任何用户定义的运算符重载.

• 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# 中，这取决于.除非有处理它的重载运算符，否则 == 将表现得像 Java(即比较引用相等性).但是，如果存在与 a 和 b 的 compile-time 类型匹配的重载(例如，如果它们都声明为字符串)，则将调用该重载.这可以按照它想要的方式运行，但它通常实现值相等(即 a 和 b 可以指代不同但 equalem> 值，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) 将调用虚拟的 Equals/Object 声明的equals 方法，除非a 的编译时类型引入了更具体的重载.这可能会或可能不会在 a 引用的对象的执行时类型中被覆盖.在 .NET 和 Java 中，Object 中的实现也会检查身份.请注意，这取决于执行时间类型，而不是重载解析所依赖的编译时间类型.

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 null 那么当你尝试时你会得到一个 NullReferenceException/NullPointerException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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