在 equals 方法中进行转换 [英] Casting in equals method

问题描述

我有一个关于在 Java 中覆盖 equals 方法的问题.在我的书中，我有以下示例:

I have a question about overriding the equals method in Java. In my book, I have the following example:

public class Dog{
     private String name;
     private int age;

public boolean equals(Object obj) {
    if(!(obj instanceof Dog)) return false;
    Dog other = (Dog) obj;                    ---> confused here
    if(this.name.equals(other.name) && (this.age == other.age) {
     return true;
    }
    else {
     return false;
    }
  }
}

我不明白为什么必须将引用强制转换为 Dog 引用.如果该引用不是 Dog 类型，我们将返回 false.为什么要投射它那么麻烦?

I don't understand why why have to cast the reference to the Dog reference. If that reference is not of type Dog we return false. Why all the hassle with casting it ?

推荐答案

obj 的声明类型是 Object，所以你必须强制转换它来告诉编译器它是一只狗.

The declared type of obj is Object, so you must cast it to tell the compiler that it is a Dog.

虽然逻辑上它不能是代码中的任何其他东西，但编译器对逻辑一无所知——它只知道类型.

Although logically it can't be anything else at that point in the code, the compiler doesn't know anything about logic - it only knows about the type.

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