Java Graphics Draw Polygons Applets

A polygon is a closed figure with many lines joined one to another. The ending point of one line is the starting point to another line and finally the last point is joins with the first point.

java.awt.Graphics class comes with two methods and one constructor to draw polygons.

1. void drawPolygon(int x[], int y[], int numOfPoints): Draws an outline polygon as per the coordinates specified in the x[] and y[] arrays. The numOfPoints gives the number of points (or to say, number of elements in the array) to join.
2. void fillPolygon(int x[], int y[], int numOfPoints): Draws a solid polygon as per the coordinates specified in the x[] and y[] arrays. The numOfPoints gives the number of points (or to say, number of elements in the array) to join.
3. Polygon(int x [], int y [], int numOfPoints): This constructor draws an outline polygon as per the coordinates specified in the x[] and y[] arrays. The numOfPoints gives the number of points to join.

All the above methods are used to draw polygons.

4 styles of drawing polygon are given.

1. Using drawPolygon() with arrays.
2. Using java.awt.Polygon class.
3. Using drawLine() method.
4. Using addPoint() method.

1st style: Using drawPolygon() with arrays

Here, two arrays comprising of x-coordinates and y-coordinates are created. These two arrays are passed to drawPolygon() method of Graphics class.

File Name: DrawingPolygons.java

import java.awt.*;
import java.applet.*;
public class DrawingPolygons extends Applet
{
  public void paint(Graphics g)
  {
    int x[] = { 70, 150, 190, 80, 100 };
    int y[] = { 80, 110, 160, 190, 100 };
    g.drawPolygon (x, y, 5);

    int x1[] = { 210, 280, 330, 210, 230 };
    int y1[] = { 70, 110, 160, 190, 100 };
    g.fillPolygon (x1, y1, 5);
  }
}

File Name: DP.html

 

       
       int x[] = { 70, 150, 190, 80, 100 };
        int y[] = { 80, 110, 160, 190, 100 };
        g.drawPolygon (x, y, 5);

Two arrays of x and y are created each with 5 elements. The array objects x and y are passed to drawPolygon() method with 5 points (marked by elements) to join. Alternatively, you can join 3 or 4 points also that joins first 3 or 4 becoming a triangle and quadrilateral. Attempting to join 6 points, which do not exist, throws ArrayIndexOutOfBoundsException.

2nd style: Using java.awt.Polygon class

The above polygon can also be obtained with Polygon constructor as follows.

       int x[] = { 50, 120, 150, 60, 75 };
       int y[] = { 60, 100, 150, 180, 100 };
       Polygon p1 = new Polygon(x, y, 5);
       g.drawPolygon(p1);

All the earlier programs like drawing rectangles are illustrated with Frame. Now let us go for applet. Applet includes init(), start() and paint() methods etc. The migration steps from graphics application to applet are available in “Java AWT Radio Buttons – Applet GUI“.

3rd style: Using drawLine() method.

Each and every line of the polygon is drawn separately (with drawLine()) while attaching end-points of one line to the starting points of another. If this is not done properly, you get a open polygon figure. This is a tedious approach compared to other 3 styles.

import java.awt.*;
public class Style3Polygon extends Frame
{
  public Style3Polygon()
  {
    setTitle("Polygons by S N Rao");
    setSize(250, 350);
    setVisible(true);
  }
  public void paint(Graphics g)   
  {
    g.drawLine(30, 50, 170, 110);
    g.drawLine(170, 110, 190, 220); 
    g.drawLine(190, 220, 150, 320); 
    g.drawLine(150, 320, 30, 50);  
  }
  public static void main(String args[])
  {
    new Style3Polygon();
  }
}

Observe the line coordinates carefully. One line x1 and y1 coordinates are another line's x2, y2. Again starting line x1, y1 are last line's x2, y2; else, an open figure will be obtained.

4th style: Using addPoint() method.

Here, we use addPoint() method of Polygon class. addPoint() method takes a pair of coordinates that becomes automatically the vertex of the polygon. drawPolygon() method takes care of joining the first vertex with the last vertex.

Supporting method of Polygon class

• void addPoint(int x, int y): drawPolygon() mehod joints all the points of x and y specified in each addPoint() method.

import java.awt.*;
public class Style4Polygon extends Frame
{
  public Style4Polygon()
  {
    setTitle("Polygons by S N Rao");
    setSize(400, 300);
    setVisible(true);
  }
  public void paint(Graphics g)   
  { 
    Polygon p1 = new Polygon();
    p1.addPoint(40,50);
    p1.addPoint(160,150);
    p1.addPoint(220,140);
    p1.addPoint(175,270);
    p1.addPoint(80,90);
    g.drawPolygon(p1);
  }
  public static void main(String args[])
  {
    new Style4Polygon();
  }
}

Now, you need not worry about the coordination of each x and y values. Give any values for each addPoint() method. The points are joined by the Polygon class implicitly.

One more program on graphics with applets is available in "Drawing Circles (Graphics with Applets)".

Note: Knowledge of "applets" is required to do with this program.

Note: In applet, window closing does not require extra code. It is implicit.