向实现接口的所有类添加方法

Question

There are several classes (which I can't edit) which implement an interface, is it possible to add a method that only calls methods defined in the interface to each class that implements that interface?

(without java 8)

Answer 1

No, I don't believe so. Such a method would have to realized in the concrete class as a real method, but without access to the classes themselves you can't do that.

You might create subclasses of each, and all those subclasses could implement you new interface with the new method.

Answer 2

我不确定我是否正确，但是如果类A，B，C，...实现了接口I，并且您无法编辑A，B，C ...，并且想要添加一个方法，那么您可以用新的子类扩展每个类，每个subA，subB，subC等都可以实现新方法...

Answer 3

I don't think there is a way to do what you are asking, not without resorting to byte code manipulation anyway.

Perhaps AOP would help, you could add a point cut to the target methods of the interface.

Answer 4

If you are using Java 8 and can modify the interface, then yes:

interface Face {
    Object existing();

    default Object additional() {
        return "Hello " + existing() + "!";
    }
}

Otherwise, no, you cannot. Java does not have a feature like Javascript prototypes, C# extension methods, etc at this time.

Answer 5

Just write a static method that takes in the interface type and calls the methods:

interface Fooable
{
    void foo();
}


public class FooableExtensions
{
    public static void doSomethingToFooable( Fooable f /*, other parameters*/ )
    {
        f.foo();
    }
}

It doesn't have the fancy syntactic-sugar that C# extension methods provide, but it should do the trick.