Java Swing Walter Milner Java Swing Walter Milner

Java Swing Walter Milner Java Swing © Walter Milner 2005: Slide 1

Note - this presentation. . • often needs to refer to source code which is too big to put on a slide • So the source code is in a separate Word document • And is also given in within this presentation in the notes Java Swing © Walter Milner 2005: Slide 2

What is Swing? • A group of 14 packages to do with the UI • 451 classes as at 1. 4 (!) • Part of JFC Java Foundation Classes (compare now defunct MFC) Java Swing © Walter Milner 2005: Slide 3

Swing and the AWT • AWT = abstract windows toolkit (cross platform) • AWT = earliest version of Java GUI • eg Frame AWT not JFrame Swing • Most Swing components are 'lightweight' • Do not mix AWT and Swing • Use Swing Java Swing © Walter Milner 2005: Slide 4

Swing and threads • A thread is a lightweight process • Most Swing components are not threadsafe • Solution is to make sure all code that creates and modifies Swing components executes in the same 'event-dispatching' thread • Start a Swing application using the following code. . Java Swing © Walter Milner 2005: Slide 5

Swing and Threads - starting up public static void main(String[] args) { Swing. Utilities. invoke. Later(new Runnable() { public void run() { create. And. Show. GUI(); // << method to start it } }); } Java Swing © Walter Milner 2005: Slide 6

create. And. Show. GUI private static void create. And. Show. GUI() { //Create and set up the window. JFrame frame = new JFrame("Hi. . "); frame. set. Default. Close. Operation(JFrame. EXIT_ON_CLOSE); //Add a label. JLabel label = new JLabel("Hello World"); frame. get. Content. Pane(). add(label); //Display the window. frame. pack(); frame. set. Visible(true); } Try this out Java Swing © Walter Milner 2005: Slide 7

Layout Managers • Most Swing UIs utilise a Layout. Manager to control positioning of items • There is a choice of these which work in different ways • Initially we do without one, and position items ourselves: • frame. set. Layout(null); Java Swing © Walter Milner 2005: Slide 8

Absolute positioning JFrame frame = new JFrame("I am a JFrame"); frame. set. Default. Close. Operation(JFrame. EXIT_ON_CLOSE); frame. set. Bounds(20, 300, 100); frame. set. Layout(null); JButton butt=new JButton("Click me"); frame. get. Content. Pane(). add(butt); butt. set. Bounds(20, 200, 20); frame. set. Visible(true); Try this out - start with last example and put this in Createand. Show. GUI() Java Swing © Walter Milner 2005: Slide 9

Responding to user actions • Based on an event-handling model • New component eg a button should have a Listener specified • The Listener object is programmed to respond to Event objects coming from the component • The Listener object needs to implement the appropriate interface Java Swing © Walter Milner 2005: Slide 10

Event-handling Event object interface eg Action. Listener the listener eg JFrame when clicked component eg button during initialisation, component selects another object eg a JFrame, to be the listener executes appropriate interface method ie action. Performed Java Swing © Walter Milner 2005: Slide 11

Interfaces • An interface is a set of methods • eg the Action. Listener interface has just one method public void action. Performed(Action. Event e) • A class can declare that it implements it eg public class Main implements Action. Listener • Then it must actually define the methods in that interface • Or the compiler will complain • Classes can implement multiple interfaces Java Swing © Walter Milner 2005: Slide 12

Button click demo • See source code in Word • JButton and JLabel • click. Counts remembers the number of clicks • Class implements Action. Listener • Make JFrame, JButton and JLabel • Instantiate application object • Set to be the listener of the button Java Swing © Walter Milner 2005: Slide 13

Which button? • If have several buttons, all must link to action. Performed • How to know which button was clicked? • Use the. get. Source method of the Action. Event object Java Swing © Walter Milner 2005: Slide 14

Example which button butt 1=new JButton("Button 1"); . . butt 2 = new JButton("Button 2"); . . public void action. Performed(Action. Event e) { if (e. get. Source()==butt 1) label. set. Text("Butt 1 clicked"); else label. set. Text("Butt 2 clicked"); } Try this out Java Swing © Walter Milner 2005: Slide 15

Look and feels CDE/Motif Windows Metal Available look and feels depend on implementation Java Swing © Walter Milner 2005: Slide 16

Setting a laf try { UIManager. set. Look. And. Feel( "com. sun. java. swing. plaf. motif. Motif. Look. And. Feel" ); } catch (Exception e) { System. out. println("Cant get laf"); }. . JFrame frame = new JFrame(); This in main() - set laf as first step try. . catch. . because could fail UIManager is in java. lang Java Swing © Walter Milner 2005: Slide 17

Finding installed lafs Object a[]= UIManager. get. Installed. Look. And. Feels(); for (int i=0; i<a. length; i++) System. out. println(a[i]); Java Swing © Walter Milner 2005: Slide 18

Decorated JFrame. set. Default. Look. And. Feel. Decorated(true); . . call JFrame constructor Java Swing © Walter Milner 2005: Slide 19

Swing has a lot of classes containers things that hold other things eg JFRame controls User I/O widgets eg JButton Java Swing © Walter Milner 2005: Slide 20

Containers top level containers - JFrame JApplet JDialog general purpose containers panel scroll pane split pane tabbed pane tool bar Java Swing © Walter Milner 2005: Slide 21

JPanel ( in create. And. Show. GUI) JFrame. set. Default. Look. And. Feel. Decorated(true); JFrame frame = new JFrame("I am a JFrame"); frame. set. Default. Close. Operation(JFrame. EXIT_ON_CLOSE); frame. set. Bounds(20, 300, 100); frame. set. Layout(null); //Create a panel JPanel my. Panel = new JPanel(); my. Panel. set. Background(new Color(255, 3, 25)); my. Panel. set. Opaque(true); //Make it the content pane. frame. set. Content. Pane(my. Panel); frame. set. Visible(true); Java Swing © Walter Milner 2005: Slide 22

JPanel • Is a subclass of JComponent • So are all the other Swing components except the top-level containers • You can add a border • And a tool-tip Java Swing © Walter Milner 2005: Slide 23

Tooltip and border . . my. Panel. set. Opaque(true); my. Panel. set. Tool. Tip. Text("I'm a JPanel"); my. Panel. set. Border(Border. Factory. create. Line. Border(Color. white)); frame. set. Content. Pane(my. Panel); . . Java Swing © Walter Milner 2005: Slide 24

JSplit. Pane. . set. Layout(null); //Create a split pane JSplit. Pane my. Pane = new JSplit. Pane(); my. Pane. set. Opaque(true); frame. set. Content. Pane(my. Pane); frame. set. Visible(true); Java Swing © Walter Milner 2005: Slide 25

JSplit. Pane with JPanels //Create a split pane JSplit. Pane my. Pane = new JSplit. Pane(); my. Pane. set. Opaque(true); my. Pane. set. Divider. Location(150); // make two panels JPanel right = new JPanel(); right. set. Background(new Color(255, 0, 0)); JPanel left = new JPanel(); left. set. Background(new Color(0, 255, 0)); // set as left and right in split my. Pane. set. Right. Component(right); my. Pane. set. Left. Component(left); Java Swing © Walter Milner 2005: Slide 26

Exercise • Program this • The buttons set the colour of the left hand pane Java Swing © Walter Milner 2005: Slide 27

JText. Field • For single-line text input • Methods get. Text, set. Text • Can use Action. Listener, triggered when Enter pressed Java Swing © Walter Milner 2005: Slide 28

Example of JText. Field • • See source in Word doc Check Main object fields for label and textfield Make a panel, set as content pane Make and add text field Add actionlistener Make and add a label Program action. Performed Java Swing © Walter Milner 2005: Slide 29

JText. Area JPanel my. Panel = new JPanel(); app. text. Area = new JText. Area("Type here", 5, 20); my. Panel. add(app. text. Area); Text. Area expands rows and columns as needed Java Swing © Walter Milner 2005: Slide 30

JScroll. Pane JText. Area text. Area = new JText. Area("Type here", 5, 20); JScroll. Pane scroll. Pane = new JScroll. Pane(text. Area); frame. set. Content. Pane(scroll. Pane); Java Swing © Walter Milner 2005: Slide 31

Exercise • Program this • Use the select. All and cut methods of JText. Component, which JText. Area inherits Java Swing © Walter Milner 2005: Slide 32

. . Timer t = new Timer(1000, app); t. start(); app. label = new JLabel("Time"); app. label. set. Bounds(20, 200, 20); frame. get. Content. Pane(). add(app. label); . . public void action. Performed(Action. Event e) { String now = (new java. util. Date()). to. String(); label. set. Text(now); } Timer Java Swing © Walter Milner 2005: Slide 33

Images JFrame frame = new JFrame("I am Celsius"); frame. set. Default. Close. Operation(JFrame. EXIT_ON_CLOSE); frame. set. Bounds(20, 30, 200); frame. get. Content. Pane(). set. Layout(null); Image. Icon icon = new Image. Icon("c: /celsius. jpg", "Celsius"); JLabel label = new JLabel(icon); label. set. Bounds(20, 150, 150); frame. get. Content. Pane(). add(label); frame. set. Visible(true); Java Swing © Walter Milner 2005: Slide 34

JScroll. Bar See source code JScroll. Bar and JLabel Constructor arguments implements Adjustment. Listener adjustment. Value. Changed e. get. Value() Java Swing © Walter Milner 2005: Slide 35

Exercise • Program this • The scroll bars determine the red, green and blue components of the background of the panel Java Swing © Walter Milner 2005: Slide 36

JCheck. Box • See source code • implements Action. Listener • is. Selected() Java Swing © Walter Milner 2005: Slide 37

Exercise • Program this • The checkbox determines if the text in the label is left or right aligned Java Swing © Walter Milner 2005: Slide 38

Radio. Button • Come in groups – only 1 selected per group • See demo code • Make radiobuttons • Make group • Add radiobuttons to group • Action. Listener Java Swing © Walter Milner 2005: Slide 39

Radio. Button Exercise • Modify the demo by adding more colour options Java Swing © Walter Milner 2005: Slide 40

Radio. Button group border. . JPanel group. Panel = new JPanel(); group. Panel. set. Bounds(10, 100, 60); group. Panel. set. Border(Border. Factory. create. Line. Border( Color. black)); frame. get. Content. Pane(). add(group. Panel); group. Panel. add(app. choice 1); group. Panel. add(app. choice 2); . . Java Swing © Walter Milner 2005: Slide 41

List. Box • • • See source code Data held in array List box shows array List box inside scroll pane my. List. get. Model(). get. Element. At(. . Java Swing © Walter Milner 2005: Slide 42

Two JList. Boxes • • See source code We want to add items to list So use a Vector not an array to hold data Check methods to delete items and copy to other listbox Java Swing © Walter Milner 2005: Slide 43

Exercise • Add a button to the last example which deletes selected items in the second list box Java Swing © Walter Milner 2005: Slide 44

Layout Managers • A layout manager controls the positioning of components • Components have a 'preferred size' so can avoid sizing them • . pack() adjusts size of a container to fit components Java Swing © Walter Milner 2005: Slide 45

Some Layout. Managers from Swing tutorial on java. sun. com Java Swing © Walter Milner 2005: Slide 46

Flow. Layout JFrame. set. Default. Look. And. Feel. Decorated(true); JFrame frame = new JFrame("Flow. Layout"); frame. set. Default. Close. Operation(JFrame. EXIT_ON_CLOSE); frame. get. Content. Pane(). set. Layout(new Flow. Layout()); JButton b 1 = new JButton("Hello"); frame. get. Content. Pane(). add(b 1); JButton b 2 = new JButton("Two"); frame. get. Content. Pane(). add(b 2); JText. Field t 1 = new JText. Field("Text here"); frame. get. Content. Pane(). add(t 1); Try this frame. pack(); Try re-sizing the frame at runtime frame. set. Visible(true); Add more buttons Add frame. set. Bounds Remove pack(); Java Swing © Walter Milner 2005: Slide 47

Border. Layout JFrame. set. Default. Look. And. Feel. Decorated(true); JFrame frame = new JFrame("Border"); frame. set. Default. Close. Operation(JFrame. EXIT_ON_CLOSE); JButton b 1 = new JButton("At the top"); frame. get. Content. Pane(). add(b 1, Border. Layout. PAGE_START ); JButton b 2 = new JButton("Bottom"); frame. get. Content. Pane(). add(b 2, Border. Layout. PAGE_END); JText. Field t 1 = new JText. Field("Left"); frame. get. Content. Pane(). add(t 1, Border. Layout. LINE_START); JText. Field t 2 = new JText. Field("Right"); frame. get. Content. Pane(). add(t 2, Border. Layout. LINE_END); JButton b 3 = new JButton("Centre"); frame. get. Content. Pane(). add(b 3, Border. Layout. CENTER ); Try this frame. pack(); frame. set. Visible(true); Java Swing © Walter Milner 2005: Slide 48

Grid JFrame. set. Default. Look. And. Feel. Decorated(true); JFrame frame = new JFrame("Grid"); frame. set. Default. Close. Operation(JFrame. EXIT_ON_CLOSE); frame. get. Content. Pane(). set. Layout(new Grid. Layout(4, 3, 5, 5)); for (int i=0; i<10; i++) frame. get. Content. Pane(). add(new JButton(""+i)); frame. pack(); frame. set. Visible(true); Java Swing © Walter Milner 2005: Slide 49

Combination layouts • • • See source code Frame is null layout Frame has an upper and lower panel Upper panel null layout Lower panel is grid layout Note font of display Java Swing © Walter Milner 2005: Slide 50

Menus JMenu. Bar JMenu. Item Java Swing © Walter Milner 2005: Slide 51

Menu Main app = new Main(); . . JMenu. Bar my. Menu. Bar = new JMenu. Bar(); JMenu menu 1 = new JMenu("File"); JMenu. Item item = new JMenu. Item("Exit"); item. add. Action. Listener(app); menu 1. add(item); my. Menu. Bar. add(menu 1); frame. set. JMenu. Bar(my. Menu. Bar); . . public void action. Performed(Action. Event e) { System. exit(0); } Java Swing © Walter Milner 2005: Slide 52

Menu Options • See source code Exercise Copy this Add a second option 'Edit' after 'File' Put choices Undo, Redo, Cut Copy and Paste in it Use appropriate icons if possible Java Swing © Walter Milner 2005: Slide 53

JTool. Bar. . frame is Border. Layout. . JTool. Bar tool. Bar = new JTool. Bar("Test"); JButton butt 1 = new JButton(new Image. Icon("icon. gif")); tool. Bar. add(butt 1); . . frame. add(tool. Bar, Border. Layout. PAGE_START); Java Swing © Walter Milner 2005: Slide 54

paint • JComponents have a paint() method • This is called by the system when it needs to display the object • Initially and eg after a re-size • You can over-ride paint() to control the appearance of the component • This implies you sub-class the component • The paint method has a Graphics object as a parameter • This is a context eg color, font etc • You tell the Graphics object to show things Java Swing © Walter Milner 2005: Slide 55

public class My. Frame extends JFrame { public My. Frame() { super("Some title"); set. Default. Close. Operation(EXIT_ON_CLOSE); set. Bounds(20, 30, 230, 180); my. Panel = new My. Panel(); my. Panel. set. Opaque(true); set. Content. Pane(my. Panel); set. Visible(true); } My. Panel my. Panel; } Example public class My. Panel extends JPanel { public void paint(Graphics g) { g. draw. Line(0, 0, get. Width(), get. Height()); g. draw. String("Hello", get. Width()/2, get. Height()/2); } } Java Swing © Walter Milner 2005: Slide 56