Advanced Java Programming

Transcription

1 Advanced Java Programming Shmulik London Lecture #5 GUI Programming Part I AWT & Basics Advanced Java Programming / Shmulik London 2006 Interdisciplinary Center Herzeliza Israel 1

2 Agenda AWT & Swing AWT components Containers Layout Managers Event Handling Painting Advanced Java Programming / Shmulik London

3 AWT & Swing Originally Java came with the AWT (Abstract Window Toolkit) AWT was very basic. Developers wanted more. Swing is a much richer API for GUI. They are built around different design concept AWT and Swing co-exist now, but you normally use Swing. Advanced Java Programming / Shmulik London

4 AWT AWT meant to be small and simple Allow easy porting to many platforms Developing GUI platform is a lot of effort JDK1.1 AWT 141 files, lines of code JDK1.5 AWT+Swing 1017 files, 209,908 lines!! JDK1.1 was light 8Mb compared to 55Mb today It was built around the concept that the GUI should have the look & feel of underlying platform A problematic concept for complex thing as GUI Advanced Java Programming / Shmulik London

5 Concept behind AWT Use underlying widgets of platform Each component in AWT is just a wrapper for an underlying native widget (its peer) The component request the windowing system to create the underlying widget and customize it according to its properties Can support only lowest common denominator of all platforms Good performance Easy to port JDK Native look & feel Too elementary Heavy weight components Difficult to write apps that will look good on different platforms Advanced Java Programming / Shmulik London

6 Some AWT components Button Frame TextField Label Scrollbar Choice others... Advanced Java Programming / Shmulik London

7 Class component All components are derived from the class java.awt.component Component Button TextComponent... TextArea TextField Advanced Java Programming / Shmulik London

8 Class Component Class component defines the properties common to all components: location, size, background color, foreground color, visibility,... public Dimension getsize() public void setsize(dimension d) public void setsize(int x, int y) public Point getlocation() public void setlocation(point p) public void setlocation(int x, int y) public Color getbackground() public void setbackground(color c)... Advanced Java Programming / Shmulik London

9 Container Container is a subclass of Component that is a superclass for all Components that can contain other components. It adds to Component the functionality of adding/removing components public void add(component c) public void remove(component c) public Component[] getcomponents() public int getcomponentcount() public void setlayout(...)... Advanced Java Programming / Shmulik London

10 Opening a Frame // A sample program that opens a yellow frame class FrameExample { public static void main(string[] args) { Frame frame = new Frame( Example ); frame.setsize(400,300); frame.setbackground(color.yellow); frame.setvisible(true); Advanced Java Programming / Shmulik London

11 Opening a Frame // A sample program that opens a yellow frame class FrameExample { public static void main(string[] args) { new SampleFrame().setVisible(true); class SampleFrame extends Frame { public SampleFrame() { super( Example ); setsize(400,300); setbackground(color.yellow); Advanced Java Programming / Shmulik London

12 Adding components // A sample program that opens a frame with // a button on it class FrameExample extends Frame{ public FrameExample () { setsize(400,300); Button okbutton = new Button( OK ); add(okbutton); public static void main(string[] args) { new FrameExample().setVisible(true); Advanced Java Programming / Shmulik London

13 Layout Managers Were are the components added? There are two ways to layout components on a container: Set the exact size and location of every component Use a LayoutManager Every container has its own LayoutManager object The LayoutManager is responsible for the the layout of the component inside the container The LayoutManager is consulted whenever there is a need to rearrange the components inside the container (container size changed, component added.. ) Advanced Java Programming / Shmulik London

14 Layout Managers add(new Button( Ok )) Frame layoutcontainer(this) FlowLayout Advanced Java Programming / Shmulik London

15 Layout Managers There a various types of Layout Managers. Each has its strategy for arranging the components. Layout managers given with java.awt: FlowLayout, BorderLayout, GridLayout, CardLayout, GridBagLayout You can define your own layout managers by implementing the interface java.awt.layoutmanager LayoutManager is an example of the Strategy pattern Advanced Java Programming / Shmulik London

16 FlowLayout setlayout(new FlowLayout()); add(new Label( Name: )); add(new TextField(10)); add(new Button( Ok )); Advanced Java Programming / Shmulik London

17 GridLayout setlayout(new GridLayout(2,2)); add(new Button( A )); add(new Button( B )); add(new Button( C )); add(new Button( D )); Advanced Java Programming / Shmulik London

18 GridLayout setlayout(new BorderLaout()); add(new Button( North ), BorderLayout.NORTH); add(new Button( East ), BorderLayout.EAST); add(new Button( South ), BorderLayout.SOUTH); add(new Button( West ), BorderLayout.WEST); add(new Button( Center ), BorderLayout.CENTER); Advanced Java Programming / Shmulik London

19 Combination of layouts Frame with BorderLayout Panel with setlayout(new BorderLaout()); GridLayout TextField display = new TextField(); add(display, BorderLayout.NORTH); Panel buttonspanel = new Panel(); buttonspanel.setlayout(new GridLayout(4,4)); String[] labels = { 7, 8, 9, +, 4, 5,... ; for (int i=0; i<labels.length; i++) { buttonspanel.add(new Button(labels[i])); Advanced Java Programming / Shmulik London

20 Graphics Every component can serve as a graphical context In order to draw on a component, you override its paint method to define the drawing. You don t call the paint method, it is called automatically by the windowing system whenever there is a need to display the component paint receives as parameter a Graphics object which has methods for drawing on the component Graphics is another example for the Strategy pattern Advanced Java Programming / Shmulik London

21 Graphics import java.awt.*; // A frame that displays some graphics on it class GraphicsExample extends Frame { public void paint(graphics painter) { painter.setcolor(color.black); painter.drawline(20,20,400,300); painter.setcolor(color.blue); painter.drawrect(50,50,150,100); painter.setcolor(color.yellow); painter.filloval(250,100,80,80); painter.setcolor(color.green); painter.fillrect(100,200,150,100); Advanced Java Programming / Shmulik London

22 Graphics Advanced Java Programming / Shmulik London

23 Graphics In order to display a drawing that is not fixed, the implementation of paint should depend on the state of the object Whenever the state changes, we need to call the repaint() method in order to refresh the display of the component. repaint() asks the windowing system to call the paint() method with the suitable graphics object. Actually, the windowing system calls the method update() which clear the display and then call the method paint(). Advanced Java Programming / Shmulik London

24 Graphics /** * A figure of a LED */ public class LEDFigure extends Component { // The state of the LED on/off private boolean ison; /** * Draws this LED. */ public void paint(graphics g) { g.setcolor(ison? Color.red.brighter() : Color.red.darker()); g.filloval(0,0,getsize().width,getsize().height); g.setcolor(color.black); g.drawoval(0,0,getsize().width,getsize().height); Advanced Java Programming / Shmulik London

25 Graphics /** * Sets the state of the LED. */ public void seton(boolean state) { ison = state; repaint(); /** * Returns the state of the LED. */ public boolean ison() { return ison; Advanced Java Programming / Shmulik London

26 Graphics LED seton() Please update my display clear display repaint() update() Windowing System paint display paint() Graphics Advanced Java Programming / Shmulik London

27 AWT event handling All components of the AWT are written as JavaBeans. You handle events fired by AWT components by registering listeners to the events they fire. The various events fired by AWT components and the interfaces of the corresponding listeners are defined in package java.awt.event You can find out which events are supported by a component by searching its API for addxxxlistener() and removexxxlistener() pairs. Advanced Java Programming / Shmulik London

28 AWT events ActionEvent ActionListener actionperformed(actionevent) TextEvent TextListener textvaluechanged(textevent) MouseEvent MouseListener mouseclicked(mouseevent) mouseentered(mouseevent) mouseexited(mouseevent) mousepressed(mouseevent) mousereleased(mouseevent) MouseMotionListener mousedragged(mouseevent) mousemoved(mouseevent) Advanced Java Programming / Shmulik London

29 ActionEvent import java.awt.*; import java.awt.event.actionevent; // A simple ActionListener that prints clicked // whenever it is notified for an ActionEvent class SimpleListener implements ActionListener { /** * Called to notify this object that some * action occured. */ public void actionperformed(actionevent event) { System.out.println( clicked ); Advanced Java Programming / Shmulik London

30 ActionEvent // An example for listening for pressing of a button class ListeningExample extends Frame { public ListeningExample() { Button okbutton = new Button( OK ); add(okbutton); pack(); ActionListener listener = new SimpleListener(); okbutton.addactionlistener(listener); public static void main(string[] args) { new ListeningExample().setVisible(true); Advanced Java Programming / Shmulik London

31 MouseEvent import java.awt.*; import java.awt.event.*; // A teasing game in which the user is encouraged // to catch a figure on the screen, but whenever // the mouse cursor gets near the figure it runs away class CatchMeGame extends Panel { // The figure the user need to catch private Component figure; // The distance beyond which the figure runs away private static final int MINIMAL_DISTANCE = 50; Advanced Java Programming / Shmulik London

32 MouseEvent public CatchMeGame() { setlayout(null); figure = new Smily(); //.. set location & dimension of figure add(figure); addmouselistener(new RunAwayAdapter(figure); public static void main(string[] args) { Frame f = new Frame( Catch me! ); f.setsize(400,300); f.add(new CatchMeGate()); f.setvisible(true); Advanced Java Programming / Shmulik London

33 MouseEvent // An adapter that listen to the movements of the mouse // and keeps the figure from being caught class RunAwayAdapter implements MouseMotionListener { private Component figure; public RunAwayAdapter(Component figure) { this.figure = figure; public void mousemoved(mouseevent event) { runaway(event.getpoint()); public void mousedragged(mouseevent event) { runaway(event.getpoint()); Advanced Java Programming / Shmulik London

34 MouseEvent private void runaway(point mouse) { //... compute the center of the figure xm,ym // if mouse if far away stay in place if (Math.abs(mouse.x-xm)>MINIMAL_DISTANCE Math.abs(mouse.y-ym)>MINIMAL_DISTANCE) { return; //.. decide for the direction of the movement figure.setlocation( figure.getlocation().x+dx, figure.getlocation().y+dy); repaint(); Advanced Java Programming / Shmulik London

35 Adapters (the need) import java.awt.*; import java.awt.event.*; /** * A panel that lets the user draw freehand lines */ public class DrawingPanel extends Panel { // The points composing the path drawn by the user java.util.list path; public DrawingPanel() { addmouselistener(new StartDrawingAdapter(this)); addmousemotionlistener(new DrawingAdapter(this)); Advanced Java Programming / Shmulik London

36 Adapters (the need) /** * Paints this component */ public void paint(graphics g) { if (path==null) { return; for (int i=0; i<path.size()-1; i++) { Point p1 = (Point)path.get(i); Point p2 = (Point)path.get(i+1); g.drawline(p1.x, p1.y, p2.x, p2.y); repaint(); Advanced Java Programming / Shmulik London

37 Adapters (the need) // Cleans the path at the beginning of the dragging class StartDrawingAdapter implements MouseListener() { private DrawingPanel target; public StartDrawingAdapter(DrawingPanel target) { this.target = target; public void mousepressed(mouseevent e) { target.path = new ArrayList(); public void mousereleased(mouseevent e) { public void mouseexited(mouseevent e) {... Advanced Java Programming / Shmulik London

38 Adapters (the need) // Adds the points to the path during the dragging class DrawingAdapter implements MouseMotionListener { private DrawingPanel target; public DrawingAdapter(DrawingPanel target) { this.target = target; public void mousedragged(mouseevent e) { target.path.add (e.getpoint()); target.repaint(); public void mousemoved(mouseevent e) { Advanced Java Programming / Shmulik London

39 Adapters In the previous example the listener classes need to implement all the method defined in the interface even though they are interested only in implementing part of them. This is a bit elaborating To avoid this, the API include for every listener interface that defines more than a single method, an adapter class that implement the interface in a trivial way. Advanced Java Programming / Shmulik London

40 Adapters package java.awt.event; /** * Adapter for MouseEvents... */ public abstract class MouseAdapter implements MouseListener{ public void mousepressed(mouseevent e) { public void mousereleased(mouseevent e) { public void mouseentered(mouseevent e) { //... mouseexited, mouseclicked as well Advanced Java Programming / Shmulik London

41 Adapters // Cleans the path at the beginning of the dragging class StartDrawingAdapter extends MouseAdapter { private DrawingPanel target; public StartDrawingAdapter(DrawingPanel target) { this.target = target; public void mousepressed(mouseevent e) { target.path = new ArrayList(); Advanced Java Programming / Shmulik London

42 Inner classes In both previous examples the main classes created adapters to act upon itself This is a common case This adds to the complexity of the code: the main object has to pass a reference of itself to the adapters the adapters has to define a field and a suitable constructor to record the target object in the adapter we make frequent use of the target reference Advanced Java Programming / Shmulik London

43 Inner classes To make the code more compact (less error prone) Java let you define inner classes Inner classes are classes defined inside the body of another class. Instance of inner-classes has automatic access to fields defined in the enclosing class, with no need to denote the reference to the enclosing object. There are several other details of inner-classes that we skip. You can read about them in the documentation of the JDK. Advanced Java Programming / Shmulik London

44 import java.awt.*; import java.awt.event.*; Inner classes /** * A panel that lets the user draw freehand lines */ public class DrawingPanel extends Panel { // The points composing the path java.util.list path; public DrawingPanel() { addmouselistener( new StartDrawingAdapter(this)); addmousemotionlistener( new DrawingAdapter(this)); Advanced Java Programming / Shmulik London

45 Inner classes /** * Paints this component */ public void paint(graphics g) { if (path==null) { return; for (int i=0; i<path.size()-1; i++) { Point p1 = (Point)path.elementAt(i); Point p2 = (Point)path.elementAt(i+1); g.drawline(p1.x, p1.y, p2.x, p2.y); repaint(); Advanced Java Programming / Shmulik London

46 Inner classes // Cleans the path at the beginning of the drag class StartDrawingAdapter extends MouseAdapter { public void mousepressed(mouseevent e) { path = new java.util.arraylist(); // Adds the points to the path during the drag class DrawingAdapter extends MouseAdapter { public void mousedragged(mouseevent e) { path.add(e.getpoint()); repaint(); Advanced Java Programming / Shmulik London

47 Anonymous classes If an inner class is needed only for a single use and its constructor gets no parameters you can define it as an anonymous class Anonymous class are defined in the place in the code were they are needed, and you immediately create an instance of the anonymous class Use anonymous classes with care - they should be used only where the code of the class is very compact 1-3 lines. Advanced Java Programming / Shmulik London

48 Anonymous classes //.. as before public class DrawingPanel extends Panel { //.. public DrawingPanel() { addmouselistener(new MouseAdapter() { public void mousepressed(mouseevent e) { path = new ArrayList(); ); addmousemotionlistener(new MouseMotionAdapter() { public void mousedragged(mouseevent e) { path.add(e.getpoint()); repaint(); ); Advanced Java Programming / Shmulik London