覆盖方法是否可以具有与基类中的访问说明符不同的访问说明符? [英] Can an overriding method have a different access specifier from that in the base class?

问题描述

在抽象类中，我必须将哪个访问修饰符用于方法，所以子类可以决定它是否应该公开?是否可以在 Java 中覆盖"修饰符?

Which access modifier, in an abstract class, do I have to use for a method, so the subclasses can decide whether it should be public or not? Is it possible to "override" a modifier in Java or not?

public abstract class A {

    ??? void method();
}

public class B extends A {
    @Override
    public void method(){
        // TODO
    }
}

public class C extends B {
    @Override
    private void method(){
        // TODO
    }
}

我知道静态绑定会有问题，如果有人打电话:

I know that there will be a problem with static binding, if someone calls:

// Will work
A foo = new B()
foo.method();

// Compiler ?
A foo = new C();
foo.method();

但也许还有另一种方式.我如何才能做到这一点?

But maybe there is another way. How I can achieve that?

推荐答案

可以放宽限制，但不能使其更具限制性:

It is possible to relax the restriction, but not to make it more restrictive:

public abstract class A {
    protected void method();
}

public class B extends A {
    @Override
    public void method(){    // OK
    }
}

public class C extends A {
    @Override
    private void method(){    // not allowed
    }
}

使原始方法 private 也不起作用，因为这种方法在子类中不可见，因此不能被覆盖.

Making the original method private won't work either, since such method isn't visible in subclasses and therefore cannot be overriden.

我建议使用 interfaces 来选择性地公开或隐藏方法:

I would recommend using interfaces to selectively expose or hide the method:

public interface WithMethod {
    // other methods
    void method();
}

public interface WithoutMethod {
    // other methods
    // no 'method()'
}

public abstract class A {
    protected void method();
}

public class B extends A implements WithMethod {
    @Override
    public void method(){
      //TODO
    }
}

public class C extends B implements WithoutMethod {
    // no 'method()'
}

...然后仅通过接口处理实例.

... then only work with the instances through the interfaces.

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