Java puzzle 24: Anonymous class demonstration

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An anonymous class is a class, which doesn’t have a name.
It is used once to override methods of a class or an interface.
For more about anonymous classes you can click here.

Note: The class Anonymous and the interface Length are two separate files in the same package.

Java puzzle 24: Anonymous class demonstration

Level: Normal

What is the output of this program and why?

Length.java

public interface Length
{
  int x = 8;
  
  void getMessage(String message);
  void getNumber(int i);
}

Anonymous.java

public class Anonymous
{
  int x = 6;
  
  public static void main(String[] args)
  {
    Anonymous an = new Anonymous();
    Length length = new Length()
    {
      public void getMessage(String str)
      {
        System.out.print(str + x);
      }
      public void getNumber(int i)
      {
        System.out.print("x" + i);
      }
    };
    length.getMessage("y");
  }
}
Author: Sar Maroof

Answer explanation

  1. The statement length.getMessage(“y”); invokes the method getMessage. The statement System.out.print(str + x); writes the parameter str and the value of the variable x to the standard output. The parameter str is y and the variable x refers to the variable x inside the interface Length. So, it writes y8 to the standard output.
  2. The method getNumber is not invoked. So, the statement System.out.print(“x” + i); will not be executed.

The answer is: y8.

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