Java puzzle 12: Passing parameters to constructors

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In this Java puzzle we pass a parameter to a constructor. I congratulate you if you can solve this puzzle!

Java puzzle 12: Passing a parameter to a constructor

Level: Hard

What is the output of this program and why?

public class MyClass
  int x = 7;
  public MyClass()
    System.out.print(" n" + x);
  public MyClass(int i)
    x += i;
    System.out.print(" p" + x);
  public int method(int i)
    x += i;
    System.out.print(" s" + x);
    return x;
  public static void main(String[] args)
    new MyClass(new MyClass().method(3));
Author: Sar Maroof

Answer explanation

  1. The statement new MyClass().method(3); instantiates an object from the class MyClass using the no-argument constructor.
    The statement x++; increments the value of x by 1, x = 7+ 1 = 8. The statement System.out.print(” n” + x); writes n8 to the standard output.
  2. The statement new MyClass().method(3) invokes the method and passes the value 3 to it. By passing the value 3, the statement x += i; increments the value of x by 3. The last value of x was 8. So, x = 8 + 3 = 11.
    The statement System.out.print(” s” + x); writes s11 to the standard output.
  3. The method method(3) returns 11 and we pass that value to a new object by using the statement new MyClass(new MyClass().method(3));
    new MyClass(11) creates an object using the one-argument constructor.
    The statement x += i; increments the value of x by i.
    Don’t forget that this is a new object that is why the value of x is 7 + 11 = 18.
    The statement System.out.print(” p” + x); writes p18 to the standard output.

The correct answer is: This program writes n8 s11 p18 to the standard output.

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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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