Java中重写方法的更宽泛的参数类型 [英] Wider argument types of overridding method in Java

问题描述

以下代码打破了OO原则？不是Java OO原则，而是一般OO原则。

What OO principle is broken by the following code ? Not Java OO principle but general OO principle.

class GeneralArg{}
class Arg extends GeneralArg{}

class A{
    public void test(Arg a){}
}

class B extends A{
    @Override
    public void test(GeneralArg a){}
}

我认为这应该有效！

但是有一个编译错误，说 B.test（）不会覆盖 A .test（）

However there is a compile error saying that B.test() doesn't override A.test()

推荐答案

你正在做的不是覆盖而是重载。

What you are doing is not overriding but overloading.

更改参数列表时重载方法。
您在更改实现时覆盖方法。

You overload a method when you change the parameter list. You override a method when you change it implementation.

    public class Foo {

       public void method1() {        
       }

       public void method1(String str) {
       //We overload method1
       }

    }

    public class Bar extends Foo {

       public void method1(String str) {
           // We override method1 here
       }

       public void method1(Number num) {
           // We overload method1 here 
       }
  }

注意，那个注释它不是强制性的，它只通知编译器您已覆盖某些方法以防止潜在的故障。

Note, that annotation is not mandatory it only inform the compiler that you have override some method to prevent potential faults.

当您在子类声明方法中使用相同的[签名]覆盖它时，当您添加/删除切换参数顺序时，您会重载。这个规则服从Java世界，因为每个非最终方法都是虚拟的，可以被覆盖。

Concluding when you in child class declare method with the same [signature] you override it, when you add/remove switch parameter order you overload. This rule obey to Java world as every not final method is virtual an can be overridden.

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