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?

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

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);
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┬áto 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┬áSystem.out.print(“x” + i); will not be executed.

The answer is: y8.

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Sar Maroof is graduated from HBO Amsterdam "higher professional education". He is a professional computer programming teacher, gives master classes and publishes technical articles. His experience with developing software started from 2001 and he has worked as a software developer for several big as well as small companies and later as a freelancer. He is the author of Java quizmaster and Build a Java application in 7 days.

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