인터페이스의 또 다른 사용 예

Main.java

import java.util.ArrayList;
import java.util.List;

public class Main implements MainFragment.OnClickListener {
    private List<Integer> mItems = new ArrayList<>();

    public Main() {
        mItems.add(10);
        mItems.add(20);
        mItems.add(30);
    }

    public static void main(String[] args) {

        Main main = new Main();
        MainFragment fragment = new MainFragment();
        fragment.mListener = main;

//        fragment.click();
        fragment.itemClick(1);
    }

    @Override
    public int onClick() {
        return 10;
    }

    @Override
    public int onItemClick(int position) {
        return mItems.get(position);
    }
}

class MainFragment {
    interface OnClickListener {
        int onClick();
        int onItemClick(int position);
    }

    OnClickListener mListener;

    public void click() {
        System.out.println("MainFragment : " + mListener.onClick());
    }

    public void itemClick(int position) {
        int value = mListener.onItemClick(position);
        System.out.println(value);
    }
}