Test Your Java Knowledge: Using Operators and Making Assignments, Part 6

I recommend that you also make use of my online Java tutorial lessons, which are designed from a more conventional textbook approach.  Those tutorial lessons are published at Gamelan.com.

For your convenience, I also maintain a consolidated Table of Contents on my personal web site that links to the individual lessons on the Gamelan site.

Insofar as possible, I will make use of Sun Java in these lessons.  However, it will not be possible for me to go back and do a full update each time Sun releases a new version, so over the course of time, I expect to use different versions of Sun Java.

Just in case you would like to sneak a peek, the answers to the questions, and the explanations of those answers are located (in reverse order) at the end of this file.

The questions and the answers are connected by hyperlinks to make it easy for you to navigate from the question to the answer and back.  It is recommended that you make your first pass through the questions in the order that they appear so as to avoid inadvertently seeing the answer to a question before you provide your own answer.

• A.  A compiler error
• B.  Exception Thrown
• C.  5
• D.  7
• E.  2
• F.  None of the above

class Q104{

  public static void main(

                        String args[]){

    try{

      byte x = 7;

      byte y = 5;

      System.out.println(x | y);

    }catch(Exception e){

      System.out.println(

                   “Exception Thrown”);

    }//end catch

  }//end main()

}//end class definition

Answer and Explanation

2.  What output is produced by the following program?

• A.  A compiler error
• B.  Exception Thrown
• C.  false true  true false false  true true false
• D.  true false  false true true  false false true
• E.  true true  false false false true true true
• F.  None of the above.

class Q105{

  public static void main(

                        String args[]){

    try{

      boolean x = true;

      boolean y = false;

      System.out.print((x & y) + ” ” +

                              (x & x));

      System.out.print(”  “);

      System.out.print(

        (x ^ y) + ” ” + (x ^ x) + ” ” +

                              (y ^ y));

      System.out.print(”  “);

      System.out.println(

        (x | y) + ” ” + (x | x) + ” ” +

                              (y | y));

    }catch(Exception e){

      System.out.println(

                   “Exception Thrown”);

    }//end catch

  }//end main()

}//end class definition

Answer and Explanation

3.  What output is produced by the following program?

• A.  A compiler error
• B.  Exception Thrown
• C.  true
• D.  false
• E.  None of the above

class Q106{

  public static void main(

                        String args[]){

    try{

      byte x = 1;

      boolean y = false;

      System.out.println(

                       (boolean)x & y);

    }catch(Exception e){

      System.out.println(

                   “Exception Thrown”);

    }//end catch

  }//end main()

}//end class definition

Answer and Explanation

4.  True or false?  Java provides “short-circuit” AND, OR, and XOR operators.

Answer and Explanation

5.  True or false?  As with the bitwise (Boolean) operators discussed in Question 2 above ( & and | ), the short-circuit logical operators ( && and || ) can be applied to either boolean or integer types.

Answer and Explanation

6.  True or false?  The following expressions describe the behavior of the short-circuit logical operators, regardless of the value of the boolean variable X.

• false && X = false
• true || X = true

Answer and Explanation

7.  True or False?  Given the following expression:

a = x ? b : c;

The following statements are all true?

• The types of the expressions b and c must be compatible and are made identical through conversion.
• The type of the expression x must be boolean.
• The type of the expressions b and c must be assignment compatible with the type of a.

The value assigned to a will be b if x is true or will be c if x is false.

Answer and Explanation

8.  What output is produced by the following program?

• A.  A compiler error
• B.  Exception Thrown
• C.  Equal
• D.  Not Equal
• E.  None of the above

class Q107{

  public static void main(

                        String args[]){

    String x = new String(“100”);

    String y = new String(“100”);

    if(x == y) 

      System.out.println(“Equal”);

    else 

      System.out.println(“Not Equal”);

  }//end main()

}//end class definition

Answer and Explanation

9.  What output is produced by the following program?

• A.  A compiler error
• B.  Exception Thrown
• C.  Equal
• D.  Not Equal
• E.  None of the above

class Q108{

  public static void main(

                        String args[]){

    String x = new String(“100”);

    String y = new String(“100”);

    if(x.equals(y)) 

      System.out.println(“Equal”);

    else 

      System.out.println(“Not Equal”);

  }//end main()

}//end class definition

Answer and Explanation

10.  What output is produced by the following program?

• A.  A compiler error
• B.  Exception Thrown
• C.  Equal
• D.  Not Equal
• E.  None of the above

class Q109{

  public static void main(

                        String args[]){

    String x = “100”;

    String y = “100”;

    if(x == y) 

      System.out.println(“Equal”);

    else 

      System.out.println(“Not Equal”);

  }//end main()

}//end class definition

Answer and Explanation

About the author

Richard Baldwin is a college professor and private consultant whose primary focus is a combination of Java and XML. In addition to the many platform-independent benefits of Java applications, he believes that a combination of Java and XML will become the primary driving force in the delivery of structured information on the Web.

Richard has participated in numerous consulting projects involving Java, XML, or a combination of the two.  He frequently provides onsite Java and/or XML training at the high-tech companies located in and around Austin, Texas.  He is the author of Baldwin’s Java Programming Tutorials, which has gained a worldwide following among experienced and aspiring Java programmers. He has also published articles on Java Programming in Java Pro magazine.

Richard holds an MSEE degree from Southern Methodist University and has many years of experience in the application of computer technology to real-world problems.

baldwin.richard@iname.com

Back to Question 10

According to Roberts, Heller, and Ernest, “Since String objects are immutable, literal strings are inevitably constant strings, so the compiler re-uses the same String object if it sees the same literal value occur more than once in the source.”

Therefore, in this case, a single literal String object gets used twice.  The reference variables x and y refer to the same literal String object.  Therefore, when x and y are tested using the == operator, the test returns true.

Back to Question 9

With respect to the String class, the equals() method can be used to determine if two objects instantiated from the class contain the same string value.  In this case, they do, so the equals() method returns true.

Back to Question 8

Back to Question 7

Back to Question 6

Back to Question 5

Back to Question 4

Back to Question 3

Back to Question 2

Back to Question 1

About the author

Richard Baldwin is a college professor and private consultant whose primary focus is a combination of Java and XML. In addition to the many platform-independent benefits of Java applications, he believes that a combination of Java and XML will become the primary driving force in the delivery of structured information on the Web.

Richard has participated in numerous consulting projects involving Java, XML, or a combination of the two.  He frequently provides onsite Java and/or XML training at the high-tech companies located in and around Austin, Texas.  He is the author of Baldwin’s Java Programming Tutorials, which has gained a worldwide following among experienced and aspiring Java programmers. He has also published articles on Java Programming in Java Pro magazine.

Richard holds an MSEE degree from Southern Methodist University and has many years of experience in the application of computer technology to real-world problems.

baldwin.richard@iname.com