F27SB2 Software Development 2 Lecture 2: Java GUIs 1

Overview Java GUIs based on 2 main class libraries AWT - Abstract Windowing Toolkit – original Java GUI classes Swing – subset of JFC - Java Foundation Classes – extends AWT – subtle but crucial differences with AWT... we will use Swing but need to be aware of AWT concepts

AWT import java.awt.*; contains original AWT GUI classes Component – main AWT class of GUI elements e.g Label, Button, TextField

Container class of Component s that can have other Component s inside them e.g. Frame – top-level displayable window e.g. Panel – Container with no display LayoutManager – interface class – control positions of nested Components

Container methods all Container s have rectangular size smallest enclosing rectangle – width – height public void setSize(int width,int height) width and height are in pixels pixel – one point on screen

Container methods size of pixel depends on – screen’s physical size diagonal in inches e.g. 15”; 17”; 21” – screen resolution number of columns/rows in pixels e.g. 1680*1050 NB make sure Container is big enough to hold everything! NB size of Containe r will change depending on properties of LayoutManager - more later

Container methods Container s may be visible or invisible public void setVisible(boolean b) make visible setVisible(true) make invisible setVisible(false) use to change Component availability e.g. turn available buttons on/off

Container methods Container s have: – background what things are drawn on e.g. paper – foreground what things are drawn in e.g pen e.g. Label

Container methods public void setBackground(Color c) set Container ’s background colour to c public void setForeground(Color c) set Container ’s foreground colour to c use these to change foreground/background dynamically at run-time

Container methods public class Color public static final Color black, blue, cyan, darkGrey, gray, green lightGray, magenta, orange, pink, red, white,yellow must preface colour identifier with Color e.g. Color.blue NB to make things in foreground disappear – set foreground to same colour as background

Basic Swing classes import javax.swing.*; many Swing classes extend AWT classes public class JComponent extends Container main Swing GUI class NB JComponents may be: opaque – can’t see through background transparent – can see through background

Basic Swing classes opacity depends on look and feel change opacity with: public void setOpaque(Boolean isOpaque) may need to setOpaque(true)

Frames public class JFrame extends Frame top-level window with: title-bar; menu-bar; cursor; icon; etc NB not a JComponent public void setTitle(String title) set title on Frame’s title bar to title

Frames to create and open a simple JFrame : class class-name extends JFrame {... public class-name(...){... } } frame is set up in a class called class-name which is an extended JFrame need an constructor for a class-name to – initialise an instance of the JFrame – hold JComponent s that make up the JFrame

Frames class program-name {... class-name frame-name;... } in the class for the main program need an instance of class-name called frame-name

Frames public static void main(String [] args) { frame-name = new class-Name(); frame-name.setTitle(“title”); frame-name.setSize(width,height); frame-name.setVisible(true); } call the constructor to instantiate frame- name to an instance of class-name give JFrame an appropriate title

Frames public static void main(String [] args) { frame-name = new class-Name(); frame-name.setTitle(“title”); frame-name.setSize(width,height); frame-name.setVisible(true); } set the JFrame ’s size to width and height – NB must allow size for title bar when specifying Frame height e.g. 20 pixels make the JFrame visible

Frames in general, cannot work directly on JFrame must manipulate the JFrame ’s ContentPane ContentPane is a Container has BorderLayout as default – more later to access ContentPane use: public Container getContentPane()

Frames e.g. 200*220 white window import java.awt.*;import javax.swing.*; class White extends JFrame { public White() { getContentPane(). setBackground(Color.white); } constructor explicitly locates ContentPane and sets background to white however, many methods will work implicitly on ContentPane e.g. add,setLayout

Frames class TestWhite { static White w; public static void main(String [] args) { w = new White(); w.setTitle(“White”); w.setSize(200,220); w.setVisible(true); } main constructs instance of White and sets up title, size and visibility

Events and listeners not yet enough to display window... need to provide further details for the operating system – what to do when window is opened or closed or iconified etc event – something that happens outside of a program listener – code that responds to an event

Events and listeners selecting window menu bar icons causes events events are detected by the Java system Java system: – stops our program – calls the appropriate listener

Events and listeners we need to... – import AWT Java event classes import java.awt.event.*; – tell the system that we have a listener for window events public void addWindowListener(WindowListener l) – build a WindowListener to respond to events

Events and listeners interface WindowListener package provides framework for building a WindowListener – abstract method defined by method signature type + name + parameters – no method body

Events and listeners interface – specification of abstract methods that implementation class will provide implementation class must provide method details

Events and listeners public interface WindowListener extends EvenListener { public void windowActivated(WindowEvent e); public void windowClosed(WindowEvent e); public void windowClosing(WindowEvent e); public void windowDeactivated(WindowEvent e); public void windowDeiconified(WindowEvent e); public void windowIconified (WindowEvent e); public void windowOpened(WindowEvent e); }

Events and listeners specific events when window is: – activated/deactivated or opened/closed or iconified/deiconified system: – calls the appropriate method from interface – provides a WindowEvent parameter to provide details of the event

Events and listeners all methods in WindowListener are abstract our class must – implement WindowListener – provide details for all methods we could implement details of all the interface methods ourselves...

Events and listeners better to: – subclass a supplied implementation of the interface – override methods we are concerned about public class WindowAdapter implements WindowListener provides empty versions of all above methods call WindowAdapter constructor – with body that defines our versions of methods – to return a WindowListener

Example e.g. 200*220 window with white background import java.awt.*; import java.awt.event.*; import javax.swing.*; class White extends JFrame { public White() { setBackground(Color.white); } }

Example class testWhite { public static void main(String [] args) { White w; w = new White(); w.setTitle(“White”); w.setSize(200,220); w.setVisible(true);...

Example... w.addWindowListener (new WindowAdapter() { public void windowClosing(WindowEvent e) { System.exit(0); } }); } } call addWindowListener – with a new WindowListener built from WindowAdapter – with a new windowClosing to exit from White

Example

Example: flashing window window flashes black to white and back every 0.5 sec repeatedly change background need some way of pausing import java.util.*; Calendar class Calendar Calendar.getInstance() returns a Calendar object which holds a snapshot of the current date and time

Example: flashing window long getTimeInMillis() returns time in milliseconds from Calendar object NB to update time, must create new Calendar object to pause: – find start time – repeatedly compare current time with start time – until required time has passed

Example: flashing window void pause(long millisecs) { long startTime = Calendar.getInstance(). getTimeInMillis(); while(Calendar. getInstance(). getTimeInMillis()- startTime<millisecs); }

Example: flashing window import java.awt.*; import java.awt.event.*; import javax.swing.*; import java.util.*; class Blackwhite extends JFrame { public Blackwhite() { getContentPane(). setBackground(Color.black); } private void pause(long millisecs){...}

Example: flashing window public void flash() { while(true) { pause(500); getContentPane(). setBackground(Color.white); pause(500); getContentPane(). setBackground(Color.black); }

Example: flashing window class TestBlackwhite { public static void main(String [] args) { static Blackwhite b; b = new Blackwhite(); b.setTitle(“Black and white”); b.setSize(200,220); b.setVisible(true);

Example: flashing window b.addWindowListener (new WindowAdapter() { public void windowClosing (WindowEvent e) { System.exit(0); } }); b.flash(); }

Example: flashing window