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Summary: Graphics
Posted on: July 27, 2006 at 12:00 AM
This is a summary of simple graphics methods in the java.awt.Graphics class for drawing with shapes, colors, text, ...

Java: Summary: Graphics

This is a summary of simple graphics methods in the java.awt.Graphics class for drawing with shapes, colors, text, ... Other classes define more advanced graphics, eg, javax.swing.Graphics2D. Related classes: Fonts, Images - ImageIcon

java.awt.Graphics Class - Basic drawing methods

Draw on a JPanel. Assume g is a Graphics object, and all variables are type int unless otherwise declared. Angles (int startAngle, arcAngle) are in degrees counterclockwise from 3 o'clock. These methods use (x,y) at the top, left, corner and a width and height of the bounding box (except drawString() and drawLine()).

g.drawLine(x1, y1, x2, y2);
g.drawRect(x, y, width, height);  // (x,y) is upper left corner 
g.fillRect(x, y, width, height);
g.drawOval(x, y, width, height);
g.fillOval(x, y, width, height); 
g.drawArc( x, y, width, height, startAngle, arcAngle);
g.fillArc( x, y, width, height, startAngle, arcAngle); 
g.drawString(String s, x, y); // Draws s with the left base at (x,y)

g.setColor(Color c);          // All drawing after this uses the Color c.
g.setFont(Font f);            // All drawing after this uses the Font f.

g.drawPolyline(int[] xPoints, int[] yPoints, nPoints); // Draws line 
g.drawPolygon( int[] xPoints, int[] yPoints, nPoints); // Draws polygon
g.drawPolygon( poly);         // draws polygon, same for fillPolygon.
g.fillPolygon( int[] xPoints, int[] yPoints, nPoints); // Fills polygon

JPanel methods

Use these calls in the constructor to set the initial values.

  setPreferredSize(new Dimension(width, height)); // Set size
  setBackground(Color c);  // Set background color
  setForeground(Color c);  // Set the initial pen color.

Use the following in paintCompenent() to get the size of the panel.

int w = this.getWidth();   // Get width of the JPanel drawing area
int h = this.getHeight();  // Get height ...

java.awt.Color Class

Predefined colors (lowercase without underscores for pre-Java 1.4) Color.BLACK, Color.WHITE, Color.DARK_GRAY, Color.GRAY, Color.LIGHT_GRAY, Color.BLUE, Color.CYAN, Color.GREEN, Color.RED, Color.MAGENTA, Color.PINK, Color.ORANGE, Color.YELLOW, Color.BLUE, Color.CYAN
Creating a color c = new Color(int r, int g, int b); // creates a new color with RGB values (each 0-255)
Example: Color mediumBlue = new Color(128, 128, 255);

java.awt.Polygon

Straight-sided shapes (eg, triangles) can be created with Polygon class and the Graphics drawPolygon or fillPolygon methods. Add each vertex as an (x, y) pair.

Polygon poly = new Polygon();  // declare and create
poly.addPoint(x, y);  // add points to polygon
. . .
g.drawPolygon(poly);

The polygon coordinates can be translated with:

poly.translate(deltaX, deltaY);

There is also a Polygon constructor which takes arrays of points:

 Polygon p = new Polygon(int[] xPoints, int[] yPoints, int nPoints);

Extend (subclass) JPanel for drawing

Drawing is usually done by defining a subclass of JPanel and overriding the paintComponent method. The constructor should set the background color and size.

import java.awt.*;
import javax.swing.*;

class MyDrawing extends JPanel {
   public MyDrawing() {  // constructor
       setBackground(Color.WHITE);
       setPreferredSize(new Dimension(200, 100));
   }
   
   public void paintComponent(Graphics g) {
       super.paintComponent(g);    // Paint background, borders
       g.drawOval(0,0, 100, 100);  // Do your drawing here.
   }
}
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