Java quiz 10: Calling constructor from constructor

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In this program we call a constructor within another constructor. Remember what happens when you create an object of a class that extends another class.

Java quiz 10: Calling constructor from constructor

Level: Normal

Note: The classes MySuper and MyClass are two separate files in one package.

What is written to the standard output as the result of executing the following code?

MySuper.java

public class MySuper
{
  MySuper()
  {
    this(2);
    System.out.print("s");
  }
  MySuper(int x)
  {
    System.out.print(x);
  }
}

MyClass.java

public class MyClass extends MySuper
{
  MyClass()
  {
    this("t");
    System.out.print("y");
  }
  MyClass(String str)
  {
    System.out.print(str);
  }
  public static void main(String[] args)
  {
    MyClass mc = new MyClass();
  }
}
                                       Author: Sar Maroof

Select the correct answer.


Answer explanation

  1. By creating the object mc, the no-argument constructor of its superclass is called.
  2. The no-argument constructor of the superclass invokes its one-argument constructor by using the statement this(2);.
  3. By passing the value 2 to the one-argument constructor, the value 2 is printed to the standard output.
  4. The statement System.out.print(“s”); prints the letter s to the standard output.
  5. The constructor of MyClass calls its one-argument constructor using the statement this(“t”);
  6. The one-argument constructor of MyClass writes the parameter t to the standard output.
  7. At last the statement System.out.print(“y”); writes y to the standard output.
    So, this program writes 2sty to the standard output.

The correct answer is: e.

 

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Sar Maroof is a professional software development teacher, gives master classes and publishes technical articles. He is also an expert software developer and worked for several big as well as small companies and later as a freelancer.

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