Directions: Give brief but precise answers to the following questions; ask if you have a question.

• Name and describe the three characteristics of object-oriented languages. (6 pts)

encapsulation - grouping related data and the methods which operate on that data

inheritance - inheriting classes get base class fields and methods automatically

polymorphism - correct like-named method chosen for related objects (see #9)

• Describe the difference between composition and inheritance and, starting with an automobile object, give an example of composition and an example of inheritance. (4 pts)

composition - where one object "has an" instance of another object within it

inheritance - where one object "is a" type of the other object

an automobile has an engine; an automobile is a motorized vehicle

• Describe, compare, and contrast abstract classes and interfaces. (5 pts)

an abstract class is a class in which at least one method has only a prototype given (not its definition); an interface is a prototype description of a promise to implement one or more methods in a class; both contain some prototype(s) (and not the definitions); an abstract class can form the basis for a single inheritance hierarchy while interfaces provide a form of "multiple inheritance" where a class can implement one or more interfaces.

• Give the first line of a Java windows application and the first line of a Java applet using the Java "swing" components. The first lines should be from the access specifier up to the opening '{' of the body. (5 pts)

public class JavaWinApp extends JFrame

public class JavaApplet extends Japplet

• Describe when the following methods init, start, paint, stop, and destroy are used. (5 pts)

init is used when an applet is created; start is used when an applet moves into sight; paint is used when an applet needs special painting; stop is used when an applet moves out of sight; and destroy is used when an applet is being unloaded.

• Describe how a button event is handled in Java (including methods and class). (5 pts)

Usually during the applet's init or the application's constructor, the button's addActionListener method is passed an object of a class which implements the interface ActionListener. This class must implement the method actionPerformed which actually handles the event when it occurs.

• Using four buttons b1, b2, b3, ... and panel(s) p1, ..., write the code to place the buttons vertically in p1 assuming BorderLayout. (5 pts)

P1.add(b1,"North");

p2.add(b2, "North"); p2.add(b3, "South"); p1.add(p2, "Center");

P1.add(b4, "South");

• Supposing that the textfield counter needs to be incremented, write statements which will accomplish this (define variables text & value). [Hint: could this involve parsing?] (5 pts)

String text = counter.getText();

int value = Integer.parseInt(text); ++value;

counter.setText("" + value);

• Describe how you can determine both named and anonymous inner classes and how their class files are named. (5 pts)

Both kinds of inner classes must be within another class declaration. The named inner class will appear as a normal class but within another class' declaration. An anonymous inner class appears inside another class' declaration but without the word class and any name; the braces of the body of the class where one would not ordinarily expect one is the key. The class file for a named inner class is simply the outer class name, a dollar sign, and the inner class name dot class. The class file for an anonymous inner class will get it name from the name of the enclosing class dollar number dot class where dollar is the dollar sign and number is a unqiue sequence number.

• Describe the purpose and format of the try and catch blocks. (5 pts)

The try and catch blocks are used for exception handling. The try block contains statements which may cause an exception and other surrounding statements. The catch block contains the exception handling code. Between the catch work and the catch block is a parenthesized list of parameters for the catch block. The try block consists of the word try following by a block (a group of statements enclosed in braces). The catch block consists of the word catch followed by parameters in braces followed by a block.

• Using the class CounterExample, the label label, the textfield counter, the button increment, and the panel panel, write a swing Java windows application to demonstrate this situation. (20 pts)

// CounterExample.java by Dr. I. for CS 102 during Spring, 1999

// This is exam 3, question 11

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

public class CounterExample extends JFrame implements ActionListener {

public CounterExample() {

setTitle("CounterExample"); setSize(200, 100);

label = new JLabel("counter");

counter = new JTextField("0", 3);

increment = new JButton("increment");

panel = new JPanel();

increment.addActionListener(this);

panel.add(label); panel.add(counter); panel.add(increment);

Container contentPane = getContentPane();

contentPane.add(panel, "Center");

}

public void actionPerformed(ActionEvent evt) {

String text = counter.getText();

int value = Integer.parseInt(text);

counter.setText("" + (value + 1));

}

public static void main(String[] args)

{ JFrame frame = new CounterExample();

frame.show();

}

private JLabel label;

private JTextField counter;

private JButton increment;

private JPanel panel;

}

• For a sport called Sport, write the class such that it will work with both our TopAthlete and TestAsgn4 classes. The evaluate method for Sport is simply the ratio of wins to the sum of wins plus losses. It should be similar to the call Wrestling. (40 pts)

// Sport.java by Dr. I. for CS 102 during Spring, 1999

// This is question #12 on exam #3

import java.util.*;

public class Sport extends Athlete {

public Sport(String name, int wins, int losses) {

super(name);

setWins(wins); setLosses(losses);

}

public int getWins() { return wins; }

public int getLosses() { return losses; }

public int evaluate() {

return (int) ((double)wins / ((double)wins + (double)losses) * 100.0);

}

public static Sport getSportAthlete() {

Inputs input = new Inputs();

System.out.print("Name? "); String name = input.readString();

System.out.print("Wins? "); int wins = input.readInt();

System.out.print("Losses? "); int losses = input.readInt();

return new Sport(name, wins, losses);

}

public static Sport getSportAthlete(String input) {

String delimiter = ":";

StringTokenizer st = new StringTokenizer(input, delimiter);

String name = st.nextToken();

int wins = Integer.parseInt(st.nextToken());

int losses = Integer.parseInt(st.nextToken());

return new Sport(name, wins, losses);

}

public String toString() {

return super.toString() + "),wins(" + wins + "),losses(" + losses + ")";

}

private void setWins(int wins) { this.wins = wins; }

private void setLosses(int losses) { this.losses = losses; }

private int wins; private int losses;

}