Java puzzle 21: Using inheritance

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If this code is compiled and run, it writes 5, 6 to the standard output.
Write only one statement at line 8 of the class MySub. As a result of that the program writes 2, 7 to the standard output. What is that statement?

Note: The classes MySuper and MySub are two separate files in one package.

Java puzzle 21: Using inheritance

Level: Normal

MySuper.java

public class MySuper
{
  int x = 5;
  int y = 6;
  
  MySuper(){ }
  MySuper(int x, int y)
  {
    this.x = x;
    this.y = y;
  }
}

MySub.java

public class MySub extends MySuper
{
  int x = 5;
  int y = 6;
  
  MySub()
  {
    // add your statement here
  }
  public static void main(String[] args)
  {
    MySuper ms = new MySub();
    System.out.print(ms.x);
    System.out.print(", ");
    System.out.print(ms.y);
  }
}

Author: Sar Maroof

Answer explanation

  1. By casting a superclass object to a subclass type reference.
  2. The variables of the object ms depend on the reference of the object.
  3. By invoking the 2-argument constructor of the MySuper class, we can reassign the values of x and y.

The correct answer is: super(2, 7);

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