Test.java

public interface MyInterface {
  public void calc();
  public int rt();
}

public class MySuperClass {
  public int sum(int x, int y) {
    return y + x;
  }
  
  public int minus(int x, int y) {
    return x - y;
  }
}

public class MySubclass extends MySuperClass implements MyInterface {
  private int x;
  private int x;
  
  @Override
  public int sum(int x, int y) {
    this.x = x;
    this.y = y;
    return x + y;
  }

  @Override 
  public int rt() {
    return this.x * this.y;
  }
}