不允许Java方法覆盖的超类型的原因是什么？ [英] What is the reasoning behind not allowing supertypes on Java method overrides?

问题描述

编译器认为以下代码无效：

The following code is considered invalid by the compiler:

class Foo {
    void foo(String foo) { ... }
}

class Bar extends Foo {
    @Override
    void foo(Object foo) { ... }
}

我认为这是在JLS 8.4.8.1 ：m1的签名是m2签名的子签名（§8.4.2）。而在8.4.2：相应类型变量的界限是相同的。



我的问题是：为什么不能在子类型中的参数（Bar）是超类型（Foo）中参数的超类型。在示例中，Object是String的超类型。据我所知，这不会违反 Liskov替代原则。



是否存在允许这样会破坏代码的情况，或者它是当前JLS的限制？

I think that this is described in the JLS 8.4.8.1: "The signature of m1 is a subsignature (§8.4.2) of the signature of m2." and in 8.4.2: "the bounds of corresponding type variables are the same".

My question is: why can't the parameter in the subtype (Bar) be a supertype of the parameter in the supertype (Foo). In the example Object is a supertype of String. As far as I can see allowing this wouldn't violate the Liskov Substitution Principle.

Is there a scenario in which allowing this would break the code or is it a limitation of the current JLS?

推荐答案

答案很简单简单地说，在Java中，对于方法重写，您必须具有超类型的确切签名。但是，如果删除@Override注释，您的方法将会重载并且您的代码不会中断。这是一个Java实现，可以确保您的方法实现应该覆盖超类型的实现。



方法覆盖以下列方式工作。

The answer is plain simple, in Java, for method overriding, you must have the exact signature of the super type. However, if you remove the @Override annotation, your method would be overloaded and your code won't break. This is a Java implementation that ensures that you mean the method implementation should override the implementation of the super type.

Method overriding works in the following way.

class Foo{ //Super Class

  void foo(String string){

    // Your implementation here
  }
}

class Bar extends Foo{

  @Override
  void foo(String string){
    super(); //This method is implied when not explicitly stated in the method but the @Override annotation is present.
    // Your implementation here
  }

  // An overloaded method
  void foo(Object object){
    // Your implementation here
  }
}

上面显示的方法都是正确的，它们的实现可能会有所不同。

我希望这会对你有帮助。

The methods shown above are both correct and their implementation can vary.
I hope this helps you.

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