Java puzzle 20: Classes and constructors

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If this code is compiled and run, it writes nullx2 to the standard output. Write only one statement at line 8. As a result of your statement the program writes xx3 to the standard output. What is that statement?

Java puzzle 20: Classes and constructors

Level: Normal

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

Answer explanation

  1. The statement should assign values to the variable i and the str object.
  2. To assign the values of the variable i and the object str in one statement, we can call the two-argument constructor. By calling a constructor inside another constructor we use the keyword this as follows.
    The correct answer is: this(“x”, 1); See the code below!
public class MyClass
{
  String str;
  int i;
  
  MyClass()
  {
    this("x", 1);
    i += 2;
    str += "x";
  }
  MyClass(String str, int i)
  {
    this.i = i;
    this.str = str;
  }
  public static void main(String[] args)
  {
    MyClass mc = new MyClass();
    System.out.print(mc.str + mc.i);
  }
}

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Sar Maroof is graduated from HBO Amsterdam “higher professional education” when he already had a bachelor of science degree in Physics.
He is a SUN certified JSP as well as EJB. He has experience with Java since 2001 and worked 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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