Java puzzle 15: Objects and methods

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If this program is compiled and run, it writes 2x to the standard output. Write only one statement on line 14. As a result of your statement the program should write 7xy to the standard output. What is that statement?

Java puzzle 15: Objects and methods

Level: Normal

public class MyClass
  int i = 2;
  String str = "x";
  void change(int i, String str)
    this.i += i;
    this.str += str;
  public static void main(String[] args)
    MyClass mc = new MyClass();
    // add your statement here
    System.out.print(mc.i + mc.str);
Author: Sar Maroof

Answer explanation

  1. The program writes 2x to the standard output.
  2. We can change the values of the variable i and the object str by using the method change.
  3. The statement mc.change(5, “y”); increments the value of i by 5. So, i = 2 + 5 = 7.
  4. The parameter y adds y to the object str which contains x already. Therefore, the value of i = 7, and the value of str = “xy”.

The answer is: mc.change(5, “y”);

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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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