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Part of a self-assessment test designed to help you determine how much you know about type conversion, casting, common exceptions, public class files, javadoc comments and directives, and null references in Java.

Table of contents

Preface

This module is part of a self-assessment test designed to help you determine how much you know about object-orientedprogramming using Java.

The test consists of a series of questions with answers and explanations of the answers.

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.

I recommend that you open another copy of this document in a separate browser window and use the links to under Listings to easily find and view the listings while you are reading about them.

Questions

Question 1 .

What output is produced by the program shown in Listing 1 ?

  • A. Compiler Error
  • B. Runtime Error
  • C. OK OK
  • D. OK
  • E. None of the above.
Listing 1 . Listing for Question 1.
public class Ap151{ public static void main(String args[]){new Worker().doIt(); }//end main()}//end class Ap151 class Worker{void doIt(){ Object refA = new MyClassA();Object refB = (Object)(new MyClassB());System.out.print(refA); System.out.print(refB);System.out.println(""); }//end doIt()}// end class Worker class MyClassA{public String toString(){ return "OK ";}//end test() }//end class MyClassAclass MyClassB{ public String toString(){return "OK "; }//end test()}//end class MyClassB

Answer and Explanation

Question 2

What output is produced by the program shown in Listing 2 ?

  • A. Compiler Error
  • B. Runtime Error
  • C. OK OK
  • D. OK
  • E. None of the above.
Listing 2 . Listing for Question 2.
public class Ap152{ public static void main(String args[]){ new Worker().doIt();}//end main() }//end class Ap152class Worker{ void doIt(){Object ref1 = new MyClassA(); Object ref2 = new MyClassB();System.out.print(ref1);MyClassB ref3 = (MyClassB)ref1; System.out.print(ref3);System.out.println(""); }//end doIt()}// end class Worker class MyClassA{public String toString(){ return "OK ";}//end test() }//end class MyClassAclass MyClassB{ public String toString(){return "OK "; }//end test()}//end class MyClassB

Answer and Explanation

Question 3

What output is produced by the program shown in Listing 3 ?

  • A. Compiler Error
  • B. Runtime Error
  • C. OK
  • D. None of the above.
Listing 3 . Listing for Question 3.
import java.util.Random; import java.util.Date;public class Ap153{ public static void main(String args[]){new Worker().doIt(); }//end main()}//end class Ap153 class Worker{void doIt(){ Random ref = new Random(new Date().getTime()); if(ref.nextBoolean()){throw new IllegalStateException(); }else{System.out.println("OK"); }//end else}//end doIt() }// end class Worker

Answer and Explanation

Question 4

What output is produced by the program shown in Listing 4 ?

  • A. Compiler Error
  • B. Runtime Error
  • C. 5 10 15
  • D. None of the above.

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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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