Class C 实现接口 B 扩展接口 A，你能说 C 实现 A 吗？

Question

In case class C implements interface B and interface B extends interface A. Is it correct to say that class C implements interface A?

Answer 1

Yes. C can override the methods of A.

Example: (It's not a good example, but it's just to show that C/Chimpanzee can override the methods of A/Animal)

interface Animal
{
    void giveBirth();
}

interface Mammal extends Animal
{
    void walk();
}

class Chimpanzee implements Mammal
{

    @Override
    public void giveBirth()
    {
        System.out.println("Chimpanzee gives birth.");
    }

    @Override
    public void walk()
    {
        System.out.println("Chimpanzee walks.");

    }
}

Answer 2

Even if I agree with the accepted answer with respect to the first part ("Yes."), I don't agree with the second part "C can override the methods of A".

I believe the correct description is that C must implement the methods of both A and B.

For example, if interface A declares the method fooA() and B declares the method fooB(), then C must implement both fooA() and fooB(). In that sense, yes, you can say that C implements interface A (since it implements an interface that extends A).

Answer 3

The accepted answer is correct. Because of polymorphism in the Java language, this is possible. , one must understand the performance impact of using the JVM instruction invokeDynamic instead of invokeVirtual . The latter on requires a simple lookup in the class's virtual table, whereas the former requires a much more in-depth recursive search through all of its implementor's virtual method tables.

Answer 4

Yes, you can say C implements A. The instanceof operator comes very handy here:

public interface B extends A {      
    public void b();    
}

public interface A {
    public void a();        
}    

public class C implements B {

@Override
public void a() {}

@Override
public void b() {}

public static void main(String[] args) {
    C c = new C();
    System.out.println("C is A? " + (c instanceof A));
    System.out.println("C is B? " + (c instanceof B));
}

}

The result will be:

C is A? true
C is B? true