Interface extending multiple interfaces

Question

i am using spring & have 2 interfaces,

interface A {
    public void a();
}

interface B {
    public void B();
}

and their implementations

class AImpl implements A {
    public void a(){ // TODO }
}
class BImpl implements B {
    public void b(){ // TODO }
}

Now I create an interface C

    interface C extends A, B {}

Is there any way I can get a bean of type C with method definations of AImpl & BImpl

TomStroemer · Accepted Answer · 2020-06-02 09:52:05Z

1

You can't make a CImpl that extends AImpl and BImpl as Java doesn't support multiple inheritance for classes.

But you can do something like this:

class CImpl implements C {
    private A a;
    private B b;

    public CImpl(A a, B b) {
        this.a = a;
        this.b = b;
    }

    public void a() {
        a.a();
    }

    public void b() {
        b.b();
    }
}

And create your CImpl with:

CImpl c = new CImpl (new AImpl(), new BImpl());

If you use Spring (as your tags imply) you can configure AImpl, BImpl and CImpl as Beans and use autowiring for the constructor of CImpl.

answered Jun 2, 2020 at 9:52

TomStroemer

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1 Comment

Praveen Gupta Over a year ago

I understand that we cannot extend the implementations directly ( as there are multiple ). But since I have already provided implementations of these interfaces (A & B), is it not possible for spring to create an object of C. This is how it happens when you create custom repository in spring jpa.

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