Question

Describe how you would develop object-oriented features of Java for the Quiz program developed in the Programming Assignments. In particular, describe how the program could use each of the following: class variables, instance variables, inheritance, polymorphism, abstract classes, "this", "super", interfaces, and event listeners.

Your Discussion should be at least 250 words in length, but not more than 750 words.

QUIZ PROGRAM EXAMPLE:
Files "QuestionDialog.java":
import java.awt.event.*;
import javax.swing.*;
public class QuestionDialog extends JDialog implements ActionListener {
String answer;
public void actionPerformed(ActionEvent e) {
answer = e.getActionCommand();
dispose();
}
}
File "Question.java":
import java.awt.*;
import javax.swing.*;
public abstract class Question {
static int nQuestions = 0;
static int nCorrect = 0;
QuestionDialog question;
String correctAnswer;
Question(String question) {
this.question = new QuestionDialog();
this.question.setLayout(new GridLayout(0,1));
this.question.add(new JLabel(" "+question+" ",JLabel.CENTER));
}
String ask() {
question.setVisible(true);
return question.answer;
}
void check() {
nQuestions++;
String answer = ask();
if (answer.equals(correctAnswer)) {
JOptionPane.showMessageDialog(null,"Correct!");
nCorrect++;
} else {
JOptionPane.showMessageDialog(null,"Incorrect. The correct
answer is "+correctAnswer+".");
}
}
void initQuestionDialog() {
this.question.setModal(true);
this.question.pack();
this.question.setLocationRelativeTo(null);
}
static void showResults() {
JOptionPane.showMessageDialog(null,nCorrect+" correct out of
"+nQuestions+" questions");
}
}
File "TrueFalseQuestion.java".
import javax.swing.*;
public class TrueFalseQuestion extends Question {
TrueFalseQuestion(String question, String answer) {
super(question);
JPanel buttons = new JPanel();
addButton(buttons,"TRUE");
addButton(buttons,"FALSE");
this.question.add(buttons);
initQuestionDialog();
answer = answer.toUpperCase();
if (answer.equals("T") || answer.equals("TRUE") || answer.equals("Y") ||
answer.equals("YES")) correctAnswer = "TRUE";
if (answer.equals("F") || answer.equals("FALSE") || answer.equals("N") ||
answer.equals("NO")) correctAnswer = "FALSE";
}
void addButton(JPanel buttons, String label) {
JButton button = new JButton(label);
button.addActionListener(question);
buttons.add(button);
}
}
File "MultipleChoiceQuestion.java"
import java.awt.*;
import javax.swing.*;
public class MultipleChoiceQuestion extends Question {
MultipleChoiceQuestion(String query, String a, String b, String c, String d, String
e, String answer) {
super(query);
addChoice("A",a);
addChoice("B",b);
addChoice("C",c);
addChoice("D",d);
addChoice("E",e);
initQuestionDialog();
correctAnswer = answer.toUpperCase();
}
void addChoice(String name, String label) {
JPanel choice = new JPanel(new BorderLayout());
JButton button = new JButton(name);
button.addActionListener(question);
choice.add(button,BorderLayout.WEST);
choice.add(new JLabel(label+" ",JLabel.LEFT),BorderLayout.CENTER);
question.add(choice);
}
}
File "Quiz.java". (This file should not have changed since the previous assignment.)
public class Quiz {
public static void main(String[] args) {
Question question = new TrueFalseQuestion("Quizzes are fun!","y");
question.check();
question = new TrueFalseQuestion("Quizzes are more fun than
programming!","n");
question.check();
question = new TrueFalseQuestion("Which one starts with T?","t");
question.check();
question = new TrueFalseQuestion("Which one starts with F?","f");
question.check();
question = new TrueFalseQuestion("Which one is not true?","false");
question.check();
question = new MultipleChoiceQuestion(
"What is a quiz?",
"a test of knowledge, especially a brief informal test given to
students",
"42",
"a duck",
"to get to the other side",
"To be or not to be, that is the question.",
"a");
question.check();
question = new MultipleChoiceQuestion("When is a quiz?",
"long, long ago",
"right now",
"the best of times",
"the worst of times",
"nevermore",
"b");
question.check();
question = new MultipleChoiceQuestion("Where is a quiz?",
"a galaxy far, far away",
"under the sea",
"right here",
"there and back again",
"the other side of the mountain",
"c");
question.check();
question = new MultipleChoiceQuestion("Why is a quiz?",
"I think, therefore it is.",
"Who is to say?",
"You tell me.",
"Because learning is fun!",
"Because I said so.",
"d");
question.check();
question = new MultipleChoiceQuestion("How is a quiz?",
"fair to middling",
"not bad",
"by a stroke of luck",
"by accident",
"Using Java object-oriented programming!",
"e");
question.check();
MultipleChoiceQuestion.showResults();
}
}

Answer 1

the pacakges are first imported in every java program

A Package is a collection of related classes. It helps organize your classes into a folder structure and make it easy to locate and use them. More importantly, it helps improve re-usability. Each package in Java has its unique name and organizes its classes and interfaces into a separate namespace, or name group
EG:import java.awt.event.*;
       import javax.swing.*;     

class variable :In object-oriented programming with classes, a class variable is any variable declared with the static modifier of which a single copy exists, regardless of how many instances of the class exist.

Note that in Java, the terms "field" and "variable" are used interchangeably for member variable.

A class variable is not an instance variable. It is a special type of class attribute (or class property, field, or data member). The same dichotomy between instance and class members applies to methods ("member functions") as well; a class may have both instance methods and class methods.

Instance variable in Java is used by Objects to store their states. Variables which are defined without the STATIC keyword and are Outside any method declaration are Object-specific and are known as instance variables.

Inheritance in Java is a mechanism in which one object acquires all the properties and behaviors of a parent object. The idea behind inheritance in Java is that you can create new classes that are built upon existing classes. When you inherit from an existing class, you can reuse methods and fields of the parent class.

Polymorphism in Java is a concept by which we can perform a single action in different ways. Polymorphism is derived from 2 Greek words: poly and morphs. The word "poly" means many and "morphs" means forms. So polymorphism means many forms.

There are two types of polymorphism in Java: compile-time polymorphism and runtime polymorphism. We can perform polymorphism in java by method overloading and method overriding.

QuestionDialog is a class which extends JDialog and implements ActionListener{(extends is a keyword of inheritance) JDialog() : creates an empty dialog without any title or any specified owner---->there are many types in JDialog

The extends keyword is mainly used to extend a class i.e. to create a subclass in Java, while implements keyword is used to implement an interface in Java.

Abtract class:An abstract class is a class that is declared abstract—it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed.

‘this’ is a reference variable that refers to the current object.

super can be used to refer immediate parent class instance variable. super can be used to invoke immediate parent class method. super() can be used to invoke immediate parent class constructor.

Interfaces:Like a class, an interface can have methods and variables, but the methods declared in an interface are by default abstract (only method signature, no body).

• Interfaces specify what a class must do and not how. It is the blueprint of the class.
• An Interface is about capabilities like a Player may be an interface and any class implementing Player must be able to (or must implement) move(). So it specifies a set of methods that the class has to implement.
• If a class implements an interface and does not provide method bodies for all functions specified in the interface, then the class must be declared abstract.
• A Java library example is, Comparator Interface. If a class implements this interface, then it can be used to sort a collection.

Event Listener:The Event listener represent the interfaces responsible to handle events. Java provides us various Event listener classes but we will discuss those which are more frequently used. Every method of an event listener method has a single argument as an object which is subclass of EventObject class. For example, mouse event listener methods will accept instance of MouseEvent, where MouseEvent derives from EventObject.

EventListner interface

It is a marker interface which every listener interface has to extend.This class is defined in java.util package.

1	ActionListener This interface is used for receiving the action events.
2	ComponentListener This interface is used for receiving the component events.
3	ItemListener This interface is used for receiving the item events.
4	KeyListener This interface is used for receiving the key events.
5	MouseListener This interface is used for receiving the mouse events.
6	TextListener This interface is used for receiving the text events.
7	WindowListener This interface is used for receiving the window events.
8	AdjustmentListener This interface is used for receiving the adjusmtent events.
9	ContainerListener This interface is used for receiving the container events.
10	MouseMotionListener This interface is used for receiving the mouse motion events.
11	FocusListener This interface is used for receiving the focus events.

IN Files "QuestionDialog.java":

what it explains is after importing packages we have created class and use inheritance and implements along with that eventlisteners. JDialog. The JDialog control represents a top level window with a border and a title used to take some form of input from the user. It inherits the Dialog class. Unlike JFrame, it doesn't have maximize and minimize buttons.

Files "QuestionDialog.java":
import java.awt.event.*;
import javax.swing.*;
public class QuestionDialog extends JDialog implements ActionListener {
String answer;
public void actionPerformed(ActionEvent e) {
answer = e.getActionCommand();
dispose();

IN File "Question.java":

Java AWT (Abstract Window Toolkit) is an API to develop GUI or window-based applications in java. Java AWT components are platform-dependent i.e. components are displayed according to the view of operating system. AWT is heavyweight i.e. its components are using the resources of OS.

Swing is a part of Java Foundation classes (JFC), the other parts of JFC are java2D and Abstract window toolkit (AWT). AWT, Swing & Java 2D are used for building graphical user interfaces (GUIs) in java. In this tutorial we will mainly discuss about Swing API which is used for building GUIs on the top of AWT and are much more light-weight compared to AWT.
used abstract class and declared variable as static type (which can be shared by all interfaces) set the layout as grid type and add new jlabel,set every question visible as true and return the answer.check the answer and retuen the dialog

as JOptionpane.showMessageDialog(null,"correct") elseJOptionPane.showMessageDialog(null,"incorrect")

File "Question.java":
import java.awt.*;
import javax.swing.*;
public abstract class Question {
static int nQuestions = 0;
static int nCorrect = 0;
QuestionDialog question;
String correctAnswer;
Question(String question) {
this.question = new QuestionDialog();
this.question.setLayout(new GridLayout(0,1));
this.question.add(new JLabel(" "+question+" ",JLabel.CENTER));
}
String ask() {
question.setVisible(true);
return question.answer;
}
void check() {
nQuestions++;
String answer = ask();
if (answer.equals(correctAnswer)) {
JOptionPane.showMessageDialog(null,"Correct!");
nCorrect++;
} else {
JOptionPane.showMessageDialog(null,"Incorrect. The correct
answer is "+correctAnswer+".");
}
}
void initQuestionDialog() {
this.question.setModal(true);
this.question.pack();
this.question.setLocationRelativeTo(null);
}
static void showResults() {
JOptionPane.showMessageDialog(null,nCorrect+" correct out of
"+nQuestions+" questions");
}
}

IN File "TrueFalseQuestion.java".

Here we have to add buttons TRUE,FALSE and actionlistenerto the buttons and also check whether the given answer is true or false and displays according to the user input.

File "TrueFalseQuestion.java".
import javax.swing.*; // check in 2
public class TrueFalseQuestion extends Question {
TrueFalseQuestion(String question, String answer) {
super(question);
JPanel buttons = new JPanel();
addButton(buttons,"TRUE");
addButton(buttons,"FALSE");
this.question.add(buttons);
initQuestionDialog();
answer = answer.toUpperCase();
if (answer.equals("T") || answer.equals("TRUE") || answer.equals("Y") ||
answer.equals("YES")) correctAnswer = "TRUE";
if (answer.equals("F") || answer.equals("FALSE") || answer.equals("N") ||
answer.equals("NO")) correctAnswer = "FALSE";
}
void addButton(JPanel buttons, String label) {
JButton button = new JButton(label);
button.addActionListener(question);
buttons.add(button);
}
}
File "MultipleChoiceQuestion.java"

this is used to display the options and add buttons,actionlistener to it. it only adds a,b,c or A,B,C,D option buttons

import java.awt.*;
import javax.swing.*;
public class MultipleChoiceQuestion extends Question {
MultipleChoiceQuestion(String query, String a, String b, String c, String d, String
e, String answer) {
super(query);
addChoice("A",a);
addChoice("B",b);
addChoice("C",c);
addChoice("D",d);
addChoice("E",e);
initQuestionDialog();
correctAnswer = answer.toUpperCase();
}
void addChoice(String name, String label) {
JPanel choice = new JPanel(new BorderLayout());
JButton button = new JButton(name);
button.addActionListener(question);
choice.add(button,BorderLayout.WEST);
choice.add(new JLabel(label+" ",JLabel.LEFT),BorderLayout.CENTER);
question.add(choice);
}
}
File "Quiz.java". (This file should not have changed since the previous assignment.)

this is used to display questions and add queries to the options a,b,c,d. And shows the result
public class Quiz {
public static void main(String[] args) {
Question question = new TrueFalseQuestion("Quizzes are fun!","y");
question.check();
question = new TrueFalseQuestion("Quizzes are more fun than
programming!","n");
question.check();
question = new TrueFalseQuestion("Which one starts with T?","t");
question.check();
question = new TrueFalseQuestion("Which one starts with F?","f");
question.check();
question = new TrueFalseQuestion("Which one is not true?","false");
question.check();
question = new MultipleChoiceQuestion(
"What is a quiz?",
"a test of knowledge, especially a brief informal test given to
students",
"42",
"a duck",
"to get to the other side",
"To be or not to be, that is the question.",
"a");
question.check();
question = new MultipleChoiceQuestion("When is a quiz?",
"long, long ago",
"right now",
"the best of times",
"the worst of times",
"nevermore",
"b");
question.check();
question = new MultipleChoiceQuestion("Where is a quiz?",
"a galaxy far, far away",
"under the sea",
"right here",
"there and back again",
"the other side of the mountain",
"c");
question.check();
question = new MultipleChoiceQuestion("Why is a quiz?",
"I think, therefore it is.",
"Who is to say?",
"You tell me.",
"Because learning is fun!",
"Because I said so.",
"d");
question.check();
question = new MultipleChoiceQuestion("How is a quiz?",
"fair to middling",
"not bad",
"by a stroke of luck",
"by accident",
"Using Java object-oriented programming!",
"e");
question.check();
MultipleChoiceQuestion.showResults();
}
}