嵌套类，实现接口对象

Question

I want to create an object KalkulatorI.AccumulatorI in a JUnit test case. When I create Kalkulator.Accumulator it's ok ( Kalkulator.Accumulator t2 = new Kalkulator().new Accumulator() ). How can I create such a interface object? I tried:

KalkulatorI.AccumulatorI t = new KalkulatorI.AccumulatorI();

or

KalkulatorI.AccumulatorI t = new KalkulatorI().new AccumulatorI();

but it doesn't work.

AccumulatorI.java :

public interface AccumulatorI {
    public int getValue();
    public void setValue(int acc);
}

KalkulatorI.java :

public interface KalkulatorI {
    public void setAccumulatorA(AccumulatorI a);
    public void setAccumulatorB(AccumulatorI a);
}

Kalkulator.java :

public class Kalkulator implements KalkulatorI {

    private AccumulatorI AA;
    private AccumulatorI BB;

    class Accumulator implements AccumulatorI{
        private int acc;

        public int getValue(){
            int res = this.acc;
            return res;
        }

        public void setValue(int acc){
            this.acc=acc;
        }
    }

    public void setAccumulatorA(AccumulatorI a){
        this.AA=a;
    }
    public void setAccumulatorB(AccumulatorI a){
        this.BB=a;
    }
}

Answer 1

You cannot instantiate interface so there is no way to call new AccumulatorI() . Please look at the Oracle's documentation