Java AWT

AWT Intro

• Abstract Windowing Toolkit
• Lib to create GUIs
• Features
  • Graphical primitives
    • draw line, fill area, text rendering
  • Event based programming (mouse/keyboard)
  • Dialogboxes
  • Advanced features
    • Bitmap rendering
    • Sound
• Portable

Swing vs. AWT

• Swing as AWT addon
• Swing has more features
• AWT easier to learn, less features
• Swing components entirely written in Java
• AWT components need native implementation

GUI Basics

• import java.awt.*
• App needs a window to display components
• Inherit from frame or dialog (subclasses of window)
• Or create a frame
• No events attached initially
• Window has standard features

Frame wnd = new Frame("My frame");
wnd.setSize(400,300);
wnd.setVisible(true);

Paint Method

• Called to draw the window
• Graphics provides a graphics device context
• Universal graphics/text output
• Provides all features (draw line, render text)
• Rendering based on 2d coord system
• (0,0) is left top corner
• unit is pixel (device dependent)
• getInsets provides current painting scope

public class AWTApp extends Frame {

    public void paint(Graphics g) {
        g.drawString("Hi!", 100, 100);
    }
}

Close a Window

• Register WindowListener
• WindowListener interface specifies a windowClosing method
• setVisible(false), System.exit(0)
• Or implement as WindowClosingAdapter (recurring task)
• And register adapter as WindowListener

public class WindowClosingAdapter extends WindowAdapter {

    @Override
    public void windowClosing(WindowEvent event) {
        event.getWindow().setVisible(false);
        event.getWindow().dispose();
        System.exit(0);
    }
}

public class Main {
    public static void main(String[] args) {
        Frame f = new Frame("WindowClosingAdapter test");
        f.addWindowListener(new WindowClosingAdapter());
        f.setSize(400,300);
        f.setLocation(100,100);
        f.setVisible(true);
    }
}

Basic Graphic Tasks

// Line
g.drawLine(x1, y1, x2, y2);

// Rectangle
// x,y is top left corner
g.drawRect(x,y, width, height);

// Polygon
// arx ... array of x coords
// ary ... array of y coords
// both arrays need to be synced
// int cnt .. num of coord pairs
g.drawPolygon(int[] arx, int[] ary, int cnt);

//Circle
// in the rect with widht and height
// with top left corner in x,y
// draw biggest ellipse
g.drawOval(int x, int y, int width, int height);

Basic Graphics Tasks #2

// Arc
// 0° - 3:00 pos
// positive angles ccw
g.drawArc(int x, int y, int width, int height, 
    int startAngle, int arcAnlge);

// Fillmodes
g.fillRect(int x, int y, int w, int h);
g.fillPolygon(int[] arx, int[] ary, int cnt);
g.fillOval(int x, int y, int width, int height);
g.fillArc(int x, int y, int width, int height,
    int startAngle, int arcAngle);

// Copy/Clear areas
g.clearRect(int x, int y, int width, int height);
g.copyArea(int x, int y, int width, int height, int dx, int dy);

Clipping Region & Text Output

// Output to certain area 
// Define smaller rects to limit "canvas"
g.clipRect(int x, int y, int width, int height);

// Define arb clip
g.setClip(int x, int y, int width, int height);

// Text output
// x,y defines basisline
g.drawString(String str, int x, int y);
g.drawChars(char[] data, int offset, int length; int x, int y);
g.drawBytes(byte[] data, int offset, int length, int x, int y),

// define different font objects
// no rotation etc. provided
// toolkit provides std fontlist
Toolkit.getDefaultToolkit().getFontList();
// Methods to get Font information

AWT Components

• Component is base class
  • abstract class, that represents a GUI element with certain size, and pos, with gui events in mind
• Container derives from Component
  • container is also component, but may hold other container
  • methods to add/remove components
  • work with layoutmanager
• Panel and Window derive from Container
• Panel used to define a set of dialog elements
• Window top-level window mit border, title and menü

AWT Frame & Visual Properties

Frame frame = new Frame("Frame");
frame.setSize(300,200);
frame.setVisible(true);

// ...
frame.setVisible(false);
frame.dispose();
System.exit(0);

• Type of border, position, size
• Relation to other windows 
• Window class has no border
• Frame has border, title and menü
• AWT provides methods to set all this data

Event Handling

• Communication between OS and app through messages
• E.g. mouseclicks, mouse movement, etc.
• Event sources: send messages
• EventListener: receive messages
• Delegation Based Event Handling
• Window class implements EventListener
• Provide callbacks
• Local anonymous EventListener classes
• Adapter class specializations

Event Handling #2

• Event types, Event objects
• Lowlevel Event: ComponentEvent subclasses
  • Transfer of basic messages between windows/dialogs
• Event listener types
• Adapter classes 
  • for every low level event source

References

Handbuch der Java-Programmierung

(5. Auflage)

Thank you for your attention!