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.

java.awt.Graphics Class

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, drawLine).

void g.drawLine(x1, y1, x2, y2);
void g.drawRect(x, y, width, height);  // (x,y) is upper left corner 
void g.fillRect(x, y, width, height);
void g.drawOval(x, y, width, height);
void g.fillOval(x, y, width, height); 
void g.drawArc( x, y, width, height, startAngle, arcAngle);
void g.fillArc( x, y, width, height, startAngle, arcAngle); 
void g.setFont(Font f);     // all drawing after this uses the Font f.
void g.drawString(String s, x, y); // draws s with the left base at (x,y)

void g.drawPolyline(int[] xPoints, int[] yPoints, nPoints); // draws line 
void g.drawPolygon( int[] xPoints, int[] yPoints, nPoints); // draws polygon
void g.drawPolygon( poly); // draws polygon, same for fillPolygon.
void g.fillPolygon( int[] xPoints, int[] yPoints, nPoints); // fills polygon
void g.setColor(Color c); // all drawing after this uses the Color c.

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.
   }
}

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);

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.Font Class to create generic fonts

In addition to the generic fonts below, you can use any of the fonts installed on the system. Get the list of available fonts using (GraphicsEnvironment.getLocalGraphicsEnvironment().getAvailableFontFamilyNames() which returns a String[]). Graphics getFontMetrics() returns info about font measurements. 
Font f;
f = new Font(String name, int style, int size);	// creates a new font
name is "Serif", "SansSerif", or "Monospaced", or a font on the system. style is Font.PLAIN. Font.BOLD, Font.ITALIC, or Font.BOLD+Font.ITALIC. size is the point size, typically in the range 8-48.
Example: 
Font big = new Font("SansSerif", Font.Bold, 48);
. . .
g.setFont(big);
g.drawString("Greetings Earthling");

Images

See Images - ImageIcon

Copyright 2004 Fred Swartz