Java quiz 25: Object references using StringBuffer

<< Java Quizzes   Green = Easy,  Blue = Normal,  Red = Hard
 Q25   Q26   Q27   Q28   Q29   Q30   Q31   Q32   Q33   Q34   Q35   Q36   Q37 
 By title 
>>

The class StringBuffer is one of the classes that you often need by writing Java programs. This example demonstrates StringBuffer and object references. If you are not familiar with the class StringBuffer, Here is a link to the article.

Java quiz 25: Object references using StringBuffer

Level: Normal
What happens if the following code is compiled and run?

public class MC
{
  public StringBuffer getSb(StringBuffer sb)
  {
    sb.append("x");
    return sb;
  }
  public static void main(String[] args)
  {
    StringBuffer sb = new StringBuffer();
    StringBuffer sb2 = new MC().getSb(sb);
    sb.append("y");
    sb2.append("z");
    System.out.print(sb + "" + sb2);
  }
}
Author: Sar Maroof

Select the correct answer.


Answer explanation

  1. The statement StringBuffer sb2 = new MyClass().getStringBuffer(sb); invokes the method getStringBuffer, which adds the letter x to the object sb.
  2. The same previous mentioned statement refers the object sb2 to the object sb, because we passed the object sb as parameter to the method and it returns the object sb. So, the statement StringBuffer sb2 = new MyClass().getStringBuffer(sb); refers the object sb2 to the object sb.
  3. So, both objects sb and sb2 refer to the same object.
  4. The statement sb.append(“y”); adds the letter y to the object sb.
  5. The statement sb2.append(“z”); adds the letter z to the object sb2.
  6. Since both object sb and sb2 are referring to the same object, the object is now contains xyz respectively.
  7. The statement System.out.print(sb + “” + sb2); writes the content of the both objects to the standard output. The result is that the code writes xyzxyz to the standard output.

The correct answer is: d.

If you found this difficult, you might consider reading my book Java quizmaster for beginners. It is easy to understand, organized to learn Java in 17 days and it guides you to master Java code by solving 105 quizzes and 117 assignments. This book explains each chapter properly before starting with exercises and assignments. It is available on Amazon. See inside the book here!

Please, leave your questions, feedback and suggestions in the comments below!
SarMaroof.com offers a practical method to learn and improve your Java skills. It avoids unnecessary long boring theoretical explanations, but it uses many exercises and quizzes.




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.

Books by Sar Maroof

           

 Subscribe to Sar Maroof's RSS feeds!
 Mail this page to a friend!
 Bookmark this page!

Leave a Reply

Your email address will not be published. Required fields are marked *

Sarmaroof © 2017