Designing Java Classes (part 4)

Shape interface

// Shape.java
// Definition of interface Shape
import java.awt.Graphics; 

public interface Shape {
	public abstract void draw(Graphics g);
	public abstract String getName();   
}

Test applet

// Test.java
// Driver for point, line, triangle hierarchy
import java.awt.Graphics; 
import javax.swing.*;

public class Test extends JApplet{
	Shape arrayOfShapes[];

	public void init()
   {
      //Circle circle = new Circle( 0.4, 0.4, 0.2 );  


      arrayOfShapes = new Shape[ 3 ];

      // aim arrayOfShapes[0] at subclass Point object
      arrayOfShapes[ 0 ] = new Point( 0.1, 0.1 );

      // aim arrayOfShapes[1] at subclass Line object
      arrayOfShapes[ 1 ] = new Line(0.1, 0.4, 0.4, 0.1);

      // aim arrayOfShapes[2] at subclass Triangle object
      arrayOfShapes[ 2 ] = new Triangle(new Point(0.1,0.8),new Point(0.8,0.6), new Point(0.8,0.2));  

   }

	public void paint(Graphics g)
	{
      for ( int i = 0; i < arrayOfShapes.length; i++ )
		  arrayOfShapes[i].draw(g);
   }
}

FrameTest Application

// FrameTest.java
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class FrameTest extends JFrame{
	Shape arrayOfShapes[];

	FrameTest(String title)
	{
		super(title);
	}

	public void init()
	{
		JPanel panel = new JPanel()
		{
			public void paint(Graphics g)
			{
				super.paint(g);
				for ( int i = 0; i < arrayOfShapes.length; i++ )
					arrayOfShapes[i].draw(g);
			}
		};
		panel.setBackground(Color.white);
		getContentPane().add(panel);

		arrayOfShapes = new Shape[ 3 ];

	  // aim arrayOfShapes[0] at subclass Point object
		arrayOfShapes[ 0 ] = new Point( 0.1, 0.1 );

	  // aim arrayOfShapes[1] at subclass Line object
		arrayOfShapes[ 1 ] = new Line(0.1, 0.4, 0.4, 0.1);

	  // aim arrayOfShapes[2] at subclass Triangle object
		arrayOfShapes[ 2 ] = new Triangle(new Point(0.1,0.8),new Point(0.8,0.6), new Point(0.8,0.1));  

	}


	public static void main( String args[])
	{
		FrameTest window = new FrameTest("Shapes");
		window.init();

		WindowAdapter wl = new WindowAdapter()
		{
			public void windowClosing( WindowEvent e )
			{
				System.exit(0);
			}
		};
		
		window.addWindowListener(wl);
		window.setSize(120,120);
		window.show();
	}		
}

Triangle class

// Triangle.java
// Definition of class Triangle (version 1)
import java.awt.Graphics; 

/**
*  Triangle describes a two-dimensional Triangle.
*
*/


public class Triangle implements Shape
{
	public Point pa = new Point();
	public Point pb = new Point();
	public Point pc = new Point();

	public Triangle() {  }

	public Triangle(Point a, Point b, Point c) { setTriangle(a,b,c); }


	public void setTriangle(Point a, Point b, Point c)
	{
		pa.setPoint(a.x,a.y);
		pb.setPoint(b.x,b.y);
		pc.setPoint(c.x,c.y);
	}


	public String getName() { return "Triangle"; }

	public void draw(Graphics g)
	{
		g.drawLine(pa.nX(),pa.nY(),pb.nX(),pb.nY());
		g.drawLine(pb.nX(),pb.nY(),pc.nX(),pc.nY());
		g.drawLine(pc.nX(),pc.nY(),pa.nX(),pa.nY());
	}
}

Line class

// Line.java
// Definition of class Line (version 1)
import java.awt.Graphics; 

/**
*  Line describes a two-dimensional line.
*
*     The line is defined by parametric equations
*
*          x(u) = pa.x * (1-u) + pb.x * u;
*          y(u) = pa.y * (1-u) + pb.y * u;
*/


public class Line implements Shape
{
	public Point pa = new Point();
	public Point pb = new Point();

	public Line() { setLine(0,0,0,0); }

	public Line(Point a, Point b) { setLine(a.x,a.y,b.x,b.y); }

	public Line(double x1, double y1, double x2, double y2)
	{
		setLine(x1,y1,x2,y2);
	}

	public void setLine(double x1, double y1, double x2, double y2)
	{
		pa.setPoint(x1,y1);
		pb.setPoint(x2,y2);
	}

	public Point getPoint(double u)
	{
		double up = 1.0-u;
		double x = pa.x * up + pb.x * u;
		double y = pa.y * up + pb.y * u;
		return new Point(x,y);
	}

	public String getName() { return "Line"; }

	public void draw(Graphics g)
	{
		g.drawLine(pa.nX(),pa.nY(),pb.nX(),pb.nY());
	}
}

Point class

// Point.java
// Definition of class Point (version 2)
import java.awt.Graphics; 

/**
*  Point describes a two-dimensional point.
*/

public class Point implements Shape
{
	static final double SCALE = 100;
	public double x, y; // coordinates of the Point

	// No-argument constructor
	public Point() { setPoint( 0, 0 ); }


	// Constructor
	public Point( double a, double b ) { setPoint( a, b ); }


	// Set x and y coordinates of Point
	public void setPoint( double a, double b )
	{
		x = a;
		y = b;
	}

	// get x pixel value
	public int nX() { return (int)(x*SCALE); }

	// get y pixel value
	public int nY() { return (int)(y*SCALE); }

	// offset (translate) point by the amount (tx, ty)
	public void offset(double tx, double ty)
	{
		x += tx;
		y += ty;
	}

	public String getName() { return "Point"; }

	public void draw(Graphics g)
	{
		int nx = nX();
		int ny = nY();
		g.fillOval(nx-5,ny-5,11,11);
	}   

   // convert the point into a String representation
   public String toString()
      { return " (" + x + ", " + y + ")"; }
}

Maintained by John Loomis, last updated 7 June 2000