Overview of AWT and Swing

To start with, you need a basic window. It is called JFrame in Swing. This is the inheritance view of JFrame. The arrow ( -> ) indicates "inherits from".

JFrame -> Frame -> Window -> Container -> Component -> Object.

JFrames can have the same "look and feel" of the native windowing framework. In other words your graphical user interface on a Macintosh will look like a Macintosh window and so on. The JFrame by itself is not enough. You need something to draw on or add components to. That functionality is provided by the class JPanel. JPanel acts like the canvas for a frame. The hierarchy for JPanel is as follows:

JPanel -> JComponent -> Container -> Component -> Object.

To draw on the canvas or JPanel you must be familiar with these three things:

• repaint() method
• paintComponent() method
• Graphics object

repaint() method is called if something has changed and you want to redraw the canvas. You can just redraw a portion of the canvas if you send a bounding box giving the coordinates of the region that needs to be redrawn.

paintComponent() method is called in response to the repaint() method. Moreover, paintComponent() is called if your window gets resized or moved.

Graphics object g is a parameter to the paintComponent() method. It is a collection of attributes. You can think of it as a pen that can write text, draw lines or fill in shapes.

Graphics

public class DrawingPanel extends JPanel {
  public void paintComponent (Graphics g) {
    g.setColor (Color.black);
    g.drawString ("Hello World!", 10, 50);
  }
  public static void main (String args[]) {
    JFrame frame = new JFrame ("Drawing Panel");
    DrawingPanel panel = new DrawingPanel();
    frame.getContentPane().add(panel);
    frame.setSize (200, 100);
    frame.setVisible (true);
    frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
  }
}

Graphics Coordinate System

Component Color and Graphics Color

public void setBackground (Color c);
public void setForeground (Color c);

You can think of the graphics object as having a pen for drawing and a paintbrush for painting. When you use the g.setColor() method you set the color of both the pen and the paintbrush. Drawing refers to making a line drawing and is usually done by calling methods of the form drawX(). Painting refers to filling a bounded object with color. Methods of the form fillX() are for painting.

Color Class

public Color (int r, int g, int b);       // range in values 0 to 255
public Color (int rgb);		          // rgb = 65536 * r + 256 * g + b
public Color (float r, float g, float b); // range in values 0.0 to 1.0

In theory it is possible to specify 256 x 256 x 256 = 16,777,216 different colors but in practice the actual colors that can be displayed depends on the quality of your system's monitor. There are 13 predefined colors - black, blue, cyan, darkGray, gray, green, lightGray, magenta, orange, pink, red, white, and yellow.

The brighter() and darker() methods enable you to start with a standard color and lighten or darken it.

Color red = Color.red;	
Color brightRed = red.brighter();
Color darkRed = red.darker();

The RGB mixture (255, 255, 255) can be used to create pure white, while (0, 0, 0) is used to specify black. Shades of gray are colors whose RGB components have equal values. Thus (128, 128, 128) is the specification for Color.gray.

Rendering Text

Font getFont();		void setFont (Font f)
Font getFontMetrics();	

The Font class defines a constructor that can be used to obtain available fonts:

Font (String name, int style, int size)

GraphicsEnvironment ge = GrahpicsEnvironment.getLocalGraphicsEnvironment();
String[] fonts = ge.getAvailableFontFamilyNames();

Supported styles include PLAIN, BOLD, ITALIC, BOLD+ITALIC. The Font() constructor is designed to work with any set of arguments. If you input the name of a font that is not available the system will supply a default font.

The FontMetrics is an object that encapsulates important data about a font such as its height and width.

Text rendering in a component is done using the following methods. The string is drawn with the baseline of the first character at the specified coordinates, using the current font and color.

void drawString (String str, int x, int y)

Drawing Lines

void drawLine ( int x1, int y1, int x2, int y2)

Drawing Rectangles

void drawRect (int x, int y, int width, int height)
void fillRect (int x, int y, int width, int height)
void drawRoundRect (int x, int y, int width, int height, int arcWidth, 
		    int arcHeight)

void draw3DRect (int x, int y, int width, int height,
			int arcWidth, int arcHeight, boolean raised)

Drawing Ovals

void drawOval (int x, int y,			// top left corner
		  int width, int height)
void fillOval (int x, int y, int width, int height)

Drawing Arcs

void drawArc (int x, int y,			// top left corner
		int width, int height,		// bounding rectangle
		int startAngle, int arcAngle)
void fillArc (int x, int y, int width, int height, 
	      int startAngle, int arcAngle)

Drawing Polygons

Polygon (int[] xpoints, int[] ypoints, int npoints)

The Graphics class provides the following methods for drawing polygons. The outline of the polygon is drawn or filled with the current color.

void drawPolygon (int[] xPoints, int[] yPoints, int nPoint)
void drawPolygon (Polygon p)
void fillPolygon (int[] xPoints, int[] yPoints, int nPoints)
void fillPolygon (Polygon p)

A polyline is an open figure, similar to a polygon, where the last vertex is not connected to the first one.

void drawPolyline (int[] xPoints, int[] yPoints, int nPoints)

Clipping

void setClip (int x, int y, int width, int height)