Java，无法降低对象继承方法的可见性 [英] Java, Cannot reduce the visibility of the inherited method from object

问题描述

继续这个问题:为什么你不能在一个 Java 子类?

我需要创建与 A 类几乎相同的 B 类，除了 B 不能做 A 的某些事情 可以.

I need to create class B that is almost identical to class A, except that B cannot do certain things that A can.

作为一个懒惰的程序员，我试图继承A，却发现B不能降低A 方法.呃！...

Being a lazy programmer as I am, I tried to inherit A, only to greet with error that B cannot reduce the visibility of A methods. Duh!..

现在A是一个厂商的API，我的目的是封装这个API，方便使用.

Now A is an API from a vendor, my intention is to encapsulate this API so that it is easier to use.

我想知道解决此问题的最佳做法是什么?

I wonder what is the best practice to work around this?

推荐答案

两个选项:

如果需要 B 保持与 A 相同的接口(以便客户端代码可以使用两者中的任何一个而无需更改)，则可以覆盖禁止"方法在 B 中并让它们抛出 UnsupportedOperationException.例如:

If you need B to keep the same interface as A (so that client code can use any of the two without changes), you can override "forbidden" methods in B and have them throw an UnsupportedOperationException. For example:

public class A
{
    public int allowedMethod() { ... }
    public int forbiddenMethod() { ... }
}

public class B extends A
{
    public int forbiddenMethod()
    {
        throw new UnsupportedOperationException("Sorry, not allowed.");
    }
}

或者，如果您真的希望 B 的 API 成为 A API 的子集，那么只需让 B 包含一个A 的实例，并适当地委托方法调用.

Or, if you really want the API of B to be a subset of the API of A, then just have B contain an instance of A, and delegate method calls appropriately.

    public class A
    {
        public int allowedMethod() { ... }
        public int forbiddenMethod() { ... }
    }

    public class B
    {
        private A a;

        public int allowedMethod()
        {
            return a.allowedMethod();
        }
    }

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