Example. Create a point class that possesses the usual attributes of x and y coordinates. In addtion, include a method to calculate the distance between two points.
//File: Pt.java
import java.text.DecimalFormat;
public class Pt
{
private double x;
private double y;
//Constructors
public Pt(double a, double
b)
{
x=a;
y=b;
}
public Pt()
{
x=0;
y=0;
}
//Accessors
public double getX()
{
return x;
}
public double getY()
{
return y;
}
//the default format for a Pt object
public String toString()
{
return "(" + x +
", " + y + ")";
}
//The following returns the distance formatted to two places after the
decimal point
public String formattedDistance(Pt p)
{
DecimalFormat precision2 = new
DecimalFormat("0.00");
return
precision2.format(distance(p));
}
public double distance(Pt p)
{
//The following implements the Pythagorean
Theorem; i.e., c squared = a squared + b squared
return
Math.sqrt(Math.pow((p.x-this.x),2) + Math.pow((p.y-this.y),2));
}
//NOTE: this.x is equivalent to x.
The keyword this refers to the current object.
}
//File: PtClient.java
import CSLib.*;
public class PtClient
{
public static void main (String [] args)
{
OutputBox out = new
OutputBox("Testing Pt Class");
out.setSize (500, 100);
Pt p1 = new Pt();
//origin (0,0)
Pt p2 = new Pt(3,4);
out.println ("The distance between "
+ p1 + " and "
+ p2 + " = " + p1.formattedDistance(p2));
}
}
Lab Exercise. Write a class for a fast food restaurant that holds hamburgers, hot dogs, and coke. Provide a constructor that starts a restaurant with no items. Include instance variables (or fields) to store the quantity of each of the three items in the restaurant. Include methods to add to the stock of each item, and a method to display the current inventory. In the main(), create two restaurants. Add items to each and display the final inventory of each restaurant.
After you try your hand, you might want to compare notes with my efforts (FastFood.java and FastFoodClient.java).
Lab Exercise. Define a class called Counter. An object of this class is used to count things, so it records a count that is a nonnegative whole number. Include methods to set the counter to zero, to increase the count by 1, and to decrease the count by 1. Be sure that no method allows the value of the counter to become negative. Also, include an accessor method that returns the current count value. Also, include a method that outputs the count to the screen. There will be no input method. The only method that can set the counter is the one that sets it to zero. Also, write a program to test your class definition.
When you're finished, take a look at my solution applied to the earlier exercise to add the numbers from 1 to n.