Source Code Files for Classes1 Examples

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/**
 * Project Kid1
 * Class Main
 * 
 * Show how to use objects created from 
 * the Kid class.  Use the default noarg
 * constructor
 */
public class Main
{
    public static void main(String[] args)
    {
        // Declare reference variable.
        Kid x;
        
        // Create object using default
        // noarg constructor.
        x = new Kid();
        
        // Declare reference variable and
        // create one object in one step.
        Kid y = new Kid();

        // Set instance variables in x.
        x.name = "Jane";
        x.gender = 'F';
        x.age = 29;
        
        // Set instance variables in y.
        y.name = "Tom";
        y.gender = 'M';
        y.age = 31;
 
        // Invoke display methods of x and y.
        x.display();
        y.display();
        
        // Invoke toString methods of x and y.
        System.out.println(x);
        System.out.println(y);
    }
}
// Output:
Name: Jane
Gender: F
Age: 29

Name: Tom
Gender: M
Age: 31

Jane F 29
Tom M 31

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/**
 * Project Kid1
 * Class Kid
 */
public class Kid
{
    // Instance variables.
    public String name;
    public char gender;
    public int age;
    
    // When no constructor is defined, the
    // default constructor is the noarg 
    // constructor that initializes 
    // (1) numeric variables to zero,
    // (2) char variables to '\0',
    // (3) String variables to null,
    // (4) boolean variables to false.
    
    // display method for printing.
    public void display()
    {
        System.out.println("Name: " + name);
        System.out.println("Gender: " + gender);
        System.out.println("Age: " + age);
        System.out.println();
    }
    
    // toString method returns object
    // information as a string.
    public String toString()
    {
        return name + " " + gender + " " + age;
    }
}

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/**
 * Project Kid2
 * Class Main
 * 
 * Show how to use objects created from 
 * the Kid class.  Use the default noarg
 * constructor
 */
public class Main
{
    public static void main(String[] args)
    {
        // Declare and create object x with
        // parameterized constructor.
        Kid x = new Kid("Jane", 'F', 29);

        // Declare and create object y with
        // parameterized constructor.
        Kid y = new Kid("Tom", 'M', 31);

        // Declare and create object z with
        // noarg constructor.
        Kid z = new Kid();
        
        // Test the getName method
        System.out.println(
            "getName method for x: " + x.getName());
       
        // Test the getGender method
        System.out.println(
            "getGender method for x: " + x.getGender());
            
         // Test the getAge method
        System.out.println(
            "getAge method for x: " + x.getAge());
        System.out.println();
 
        // Invoke toString methods of x and y.
        System.out.println(x);
        System.out.println(y);
        System.out.println(z);
        System.out.println();
        
        // Test the hasBirthday method.
        y.hasBirthday();
        
        // Text the setGender method.
        y.setGender('F');

        System.out.println(y);
    }
}
// Output:
getName method for x: Jane
getGender method for x: F
getAge method for x: 29

Jane F 29
Tom M 31
Unknown U -1

Tom F 32

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/**
 * Project Kid2
 * Class Kid
 */
public class Kid
{
    // Private instance variables.
    private String name;
    private char gender;
    private int age;
    
    // Noarg constructor;
    public Kid()
    {
        name = "Unknown";
        gender = 'U';
        age = -1;
    }
    
    // Parameterized constructor, which 
    // performs data validation.
    public Kid(String aName, char aGender, int anAge)
    {
        // Don't allow empty string as a name.
        if (aName.equals(""))
            name = "Unknown";
        else
            name = aName;
            
        // Gender must be 'F' or 'M'.
        if (aGender == 'F' || aGender == 'M')
            gender = aGender;
        else
            gender = 'U';
            
        // Age must be nonnegative.
        if (anAge < 0)
            age = -1;
        else
            age = anAge;
    }
            
    // Accessor method for name.
    public String getName()
    {
        return name;
    }
    
    // Accessor method for gender.
    public char getGender()
    {
        return gender;
    }
    
    // Accessor method for name.
    public int getAge()
    {
        return age;
    }
    
    // Mutator method for gender.
    public void setGender(char aGender)
    {
        // Gender must be 'F' or 'M'.
        if (aGender == 'F' || aGender == 'M')
            gender = aGender;
        else
            gender = 'U';
    }
    
    // hasBirthday method adds 1 to age.
    public void hasBirthday()
    {
        age++;
    }
    
    // toString method returns object
    // information as a string.
    public String toString()
    {
        return name + " " + gender + " " + age;
    }
}

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/**
 * Project Kid3
 * Class Main
 * 
 * Show how reference variables can
 * be reassigned.
 */
public class Main
{
    public static void main(String[] args)
    {
        // Declare and create object x with
        // parameterized constructor.
        Kid x = new Kid("Jane", 'F', 29);

        // Declare and create object y with
        // parameterized constructor.
        Kid y = new Kid("Tom", 'M', 31);

        // Check original values of x and y.
        System.out.println(x);
        System.out.println(y);
        System.out.println();
 
        // Reassign y.  The object "Tom" can be
        // reclaimed by the garbage collector.
        y = x;
        
        // Check new values of x and y.
        System.out.println(x);
        System.out.println(y);
        System.out.println();
        
        // Add one to age of x.
        x.hasBirthday();
        
        // Check that y is an alias for x.
        System.out.println(x);
        System.out.println(y);
        
        // Object "Jane" can be reclaimed by
        // garbage collector.
        x = null;
        y = null;
    }
}
// Output:
Jane F 29
Tom M 31

Jane F 29
Jane F 29

Jane F 30
Jane F 30

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/**
 * Project Kid3
 * Class Kid
 */
public class Kid
{
    // Private instance variables.
    private String name;
    private char gender;
    private int age;
    
    // Noarg constructor;
    public Kid()
    {
        name = "Unknown";
        gender = 'U';
        age = -1;
    }
    
    // Parameterized constructor, which 
    // performs data validation.
    public Kid(String aName, char aGender, int anAge)
    {
        // Don't allow empty string as a name.
        if (aName.equals(""))
            name = "Unknown";
        else
            name = aName;
            
        // Gender must be 'F' or 'M'.
        if (aGender == 'F' || aGender == 'M')
            gender = aGender;
        else
            gender = 'U';
            
        // Age must be nonnegative.
        if (anAge < 0)
            age = -1;
        else
            age = anAge;
    }
            
    // Accessor method for name.
    public String getName()
    {
        return name;
    }
    
    // Accessor method for gender.
    public char getGender()
    {
        return gender;
    }
    
    // Accessor method for name.
    public int getAge()
    {
        return age;
    }
    
    // Mutator method for gender.
    public void setGender(char aGender)
    {
        // Gender must be 'F' or 'M'.
        if (aGender == 'F' || aGender == 'M')
            gender = aGender;
        else
            gender = 'U';
    }
    
    // hasBirthday method adds 1 to age.
    public void hasBirthday()
    {
        age++;
    }
    
    // toString method returns object
    // information as a string.
    public String toString()
    {
        return name + " " + gender + " " + age;
    }
}

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/**
 * Project Pair1
 * Class Main
 * 
 * Illustrate how to create Pair objects with
 * overloaded constructors.
 */
public class Main
{
    public static void main(String[] args)
    {
        // Declare and create Pair objects.
        Pair u = new Pair();
        Pair v = new Pair(3);
        Pair w = new Pair(5, 8);
        
        System.out.println(u + " " + v + " " + w);
    }
}
// Output:
(0,0) (3,3) (5,8)

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/**
 * Project Pair1
 * Class Pair
 * 
 */
public class Pair
{
    // Instance variables are x and y coordinates.
    private int x, y;
    
    // Noarg constructor.
    public Pair()
    {
        x = 0;
        y = 0;
    }
    
    // Constructor with one parameter.
    public Pair(int value)
    {
        x = value;
        y = value;
    }
    
    // Constructor with two arguments.
    public Pair(int xValue, int yValue)
    {
        x = xValue;
        y = yValue;
    }
    
    // Accessor method for x.
    public int getX()
    {
        return x;
    }
    
    // Accessor method for y.
    public int getY()
    {
        return y;
    }
    
    // toString method.
    public String toString()
    {
        return "(" + x + "," + y + ")";
    }
}

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/**
 * Project Pair2
 * Class Points
 * 
 * Demonstrate the Pair display method that
 * plots points on an Applet.
 */
import java.applet.Applet;
import java.awt.*;
    
public class Points extends Applet
{
    public void init()
    {
        setBackground(Color.white);
        setSize(400, 400);
    }

    public void paint(Graphics g)
    {
        int i, x, y;
        Pair p;
        
        // Set color of Pair objects to red.
        g.setColor(Color.red);
        
        // Create and display 500 Pair objects.
        for(i = 1; i <= 500; i++)
        {
            // Pick random x value.
            x = (int) (400 * Math.random());
            
            // Pick random x value.
            y = (int) (400 * Math.random());
            
            // Create new Pair with random 
            // x, y values.
            p = new Pair(x, y);
            
            // Display point on applet.
            p.display(g);
        }
    }
}
// Display 500 random points in applet.

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/**
 * Project Pair2
 * Class Points
 * 
 * Demonstrate the Pair display method that
 * plots points on an Applet.
 */
import java.applet.Applet;
import java.awt.*;
    
public class Points extends Applet
{
    public void init()
    {
        setBackground(Color.white);
        setSize(400, 400);
    }

    public void paint(Graphics g)
    {
        int i, x, y;
        Pair p;
        
        // Set color of Pair objects to red.
        g.setColor(Color.red);
        
        // Create and display 500 Pair objects.
        for(i = 1; i <= 500; i++)
        {
            // Pick random x value.
            x = (int) (400 * Math.random());
            
            // Pick random x value.
            y = (int) (400 * Math.random());
            
            // Create new Pair with random 
            // x, y values.
            p = new Pair(x, y);
            
            // Display point on applet.
            p.display(g);
        }
    }
}

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/**
 * Project Student
 * Class Main
 * 
 * Illustrate methods that compute averages
 * of instance variables.
 */
import java.text.DecimalFormat;
    
public class Main
{
    public static void main(String[] args)
    {
        DecimalFormat df = new DecimalFormat("#0");
        Student x = new Student(
            "Jane", 100, 95, 100, 90, 85, 86, 92);
        System.out.println("x project average: " +
            df.format(x.getProjectAve()));
        System.out.println("x exam average: " +
            df.format(x.getExamAve()));
        System.out.println("x course average: " +
            df.format(x.getCourseAve()));
        System.out.println("x course grade: " +
            x.getCourseGrade());
    }
}
// Output:
x project average: 94
x exam average: 89
x course average: 91
x course grade: A

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/**
 * Project Student
 * Class Student
 * 
 * The student class contains name, project scores,
 * midterm score, and final score.  The methods
 * compute averages of the instance variables.
 */
public class Student
{
    // Instance Variables.
    private String name;
    private int proj1, proj2, proj3, proj4, proj5;
    private int midterm, fin;
    
    // Parameterized constructor.
    public Student(String n,
        int p1, int p2, int p3, int p4, int p5,
        int m, int f)
    {
        proj1 = p1;
        proj2 = p2;
        proj3 = p3;
        proj4 = p4;
        proj5 = p5;
        midterm = m;
        fin = f;
    }
    
    // Methods to compute averages.
    public double getProjectAve()
    {
        return (proj1+proj2+proj3+proj4+proj5)/5;
    }    

    public double getExamAve()
    {
        return (midterm + fin) / 2;
    }
    
    public double getCourseAve()
    {
        return (getProjectAve() + 2 * getExamAve()) / 3;
    }
    
    public char getCourseGrade()
    {
        double grade;
        grade = getCourseAve();
        if (grade >= 89.5)
            return 'A';
        else if (grade >= 79.5)
            return 'B';
        else if (grade >= 69.5)
            return 'C';
        else if (grade >= 59.5)
            return 'D';
        else
            return 'F';
    }        
}

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