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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.

Questions & Answers

the diagram of the digestive system
Assiatu Reply
How does twins formed
William Reply
They formed in two ways first when one sperm and one egg are splited by mitosis or two sperm and two eggs join together
Oluwatobi
what is genetics
Josephine Reply
Genetics is the study of heredity
Misack
how does twins formed?
Misack
What is manual
Hassan Reply
discuss biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles
Joseph Reply
what is biology
Yousuf Reply
the study of living organisms and their interactions with one another and their environments
AI-Robot
the study of living organisms and their interactions with one another and their environment.
Wine
discuss the biological phenomenon and provide pieces of evidence to show that it was responsible for the formation of eukaryotic organelles in an essay form
Joseph Reply
what is the blood cells
Shaker Reply
list any five characteristics of the blood cells
Shaker
lack electricity and its more savely than electronic microscope because its naturally by using of light
Abdullahi Reply
advantage of electronic microscope is easily and clearly while disadvantage is dangerous because its electronic. advantage of light microscope is savely and naturally by sun while disadvantage is not easily,means its not sharp and not clear
Abdullahi
cell theory state that every organisms composed of one or more cell,cell is the basic unit of life
Abdullahi
is like gone fail us
DENG
cells is the basic structure and functions of all living things
Ramadan
What is classification
ISCONT Reply
is organisms that are similar into groups called tara
Yamosa
in what situation (s) would be the use of a scanning electron microscope be ideal and why?
Kenna Reply
A scanning electron microscope (SEM) is ideal for situations requiring high-resolution imaging of surfaces. It is commonly used in materials science, biology, and geology to examine the topography and composition of samples at a nanoscale level. SEM is particularly useful for studying fine details,
Hilary
cell is the building block of life.
Condoleezza Reply
what is cell divisoin?
Aron Reply
Diversity of living thing
ISCONT
what is cell division
Aron Reply
Cell division is the process by which a single cell divides into two or more daughter cells. It is a fundamental process in all living organisms and is essential for growth, development, and reproduction. Cell division can occur through either mitosis or meiosis.
AI-Robot
What is life?
Allison Reply
life is defined as any system capable of performing functions such as eating, metabolizing,excreting,breathing,moving,Growing,reproducing,and responding to external stimuli.
Mohamed
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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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