扩展已经实现接口的抽象类的类是否需要接口？

Question

Assume there is a code as such:

package com.ps.Sample;

public interface Sample
{
    public void Method1();
}

public abstract class AbstractSample implements Sample
{
    public void Method1()
    {
        System.out.println("Hello World");
    }
}

public class MySample extends AbstractSample
{

}

public class TestSample
{
    public static void main(String[] args) 
    {
        Sample my = new MySample();

        my.Method1();
    }

}

My question is: Is there any benefit to declaring the concrete class as

public class MySample extends AbstractSample implements Sample

instead of

public class MySample extends AbstractSample 

Answer 1

No, there is not. It's redundant. AbstractSample is a Sample, and MySample is a AbstractSample. So MySample is a Sample.

The javadoc displays all the implemented interfaces anyway, whether you add the implements Sample or not.

Answer 2

一个好处是，如果将AbstractSample更改为不实现Sample，则第一个声明仍然允许您将MySample的实例传递给期望Sample的方法。