CS535: Doc 21, AWT Basics

CS535 Object-Oriented Programming & Design
Fall Semester, 1996
Doc 21, AWT Basics

[To Lecture Notes Index]
San Diego State University -- This page last updated Nov 11, 1996

Contents of Doc 21, AWT Basics

Doc 21, AWT Basics Slide # 1

References

Core Java, Chapter 6

Graphic Java, Geary and McClellan, Chapters 3, 4

Doc 21, AWT Basics Slide # 2

Building GUIs - Abstract Window Toolkit (AWT)

Overview and Basics

Types of things in AWT
Components

Basic UI things like

Buttons, Checkboxes, Choices,
Lists, Menus, and Text Fields
Scrollbars and Labels

Containers

Contain components and containers

Window

Layouts

Position items in window

Graphics

Drawing on the screen

Doc 21, AWT Basics Slide # 3

Graphics 101 Window Coordinate System

Doc 21, AWT Basics Slide # 4

First Example

import  java.awt.*;

class  HelloApplication  extends  Frame 
   {
   public  void  paint(  Graphics  display  )
      {
      int startX  =  30;
      int startY  =  40;
      display.drawString(  "Hello World", startX, startY  );
      }
   }

class Test
   {
   public  static  void  main( String  args[] )
      {
      HelloApplication  mainWindow = new  HelloApplication();

      int  HorizontalPixelSize  =  150;
      int  VerticalPixelSize  =  80;
      mainWindow.resize( HorizontalPixelSize, VerticalPixelSize );
      mainWindow.show();
      }
   }

Subclass Frame to get a window

Paint is called when window needs to be drawn

Becareful! It is hard to exit from this program
Doc 21, AWT Basics Slide # 5

Hello Again


import  java.awt.*;

class  Hello  extends  Frame 
   {
   public Hello( int width, int height, String title )
      {
      resize( width,  height );
      setTitle( title );
      show();      
      }
   public  void  paint(  Graphics  display  )
      {
      int startX  =  30;
      int startY  =  40;
      display.drawString(  "Hello World", startX, startY  );
      }
   }

class Test
   {
   public  static  void  main( String  args[] )
      {
      Hello  mainWindow = new  Hello( 150, 80, "Hi Dad");
      }
   }

Doc 21, AWT Basics Slide # 6

Quitting (already?)

import  java.awt.*;

class  HelloApplication  extends  Frame 
   {
   public  HelloApplication( int  widthInPixels, int heightInPixels )
      {
      setTitle( "Hi Mom" );
      resize( widthInPixels, heightInPixels );
      }

   public boolean handleEvent( Event userAction )
      {
      if ( userAction.id == Event.WINDOW_DESTROY )
         { 
         System.exit(0);
         return true;      // return true if you handle the event
         }
      else
         return super.handleEvent( userAction );
                  // When you don't handle the event
      }

   public  void  paint(  Graphics  display  )
      {
      int startX  =  30;
      int startY  =  40;
      display.drawString(  "Hello World", startX, startY  );
      }

   public  static  void  main( String  args[] )
      {
      HelloApplication  mainWindow; 
      mainWindow  = new  HelloApplication( 300,  200 );
      mainWindow.show();
      }
   }
Doc 21, AWT Basics Slide # 7

Result of Running Program

Doc 21, AWT Basics Slide # 8

Events

When the user does something that affects a window, an event is sent to the window

Types of things a user can do:

mouse click: type a key
move mouse: drag mouse
move windows: resize windows
press buttons: scroll a window
close windows

An event object contains:


target the part of the window the event is meant for
when the time stamp of when the event occurred
id which type of event occurred
x
y the x and y coordinate of a mouse event
key the key pressed in a keyboard event
modifiers the state of the modifier keys
arg general purpose object for transferring information

Doc 21, AWT Basics Slide # 9

What Events are There? Window Events

WINDOW_DEICONIFY	WINDOW_ICONIFY
WINDOW_DESTROY	WINDOW_MOVED
WINDOW_EXPOSE

Keyboard Events

KEY_ACTION	KEY_PRESS
KEY_ACTION_RELEASE	KEY_RELEASE

Mouse Events

MOUSE_DOWN	MOUSE_EXIT
MOUSE_DRAG	MOUSE_MOVE
MOUSE_ENTER	MOUSE_UP

Scrollbar Events

SCROLL_ABSOLUTE	SCROLL_PAGE_DOWN
SCROLL_LINE_DOWN	SCROLL_PAGE_UP
SCROLL_LINE_UP

List Events

LIST_DESELECT

LIST_SELECT

Action Events

ACTION_EVENT	LOST_FOCUS
GOT_FOCUS	SAVE_FILE
LOAD_FILE

Doc 21, AWT Basics Slide # 10

How to show events

import  java.awt.*;

class  ShowEvents  extends  Frame 
   {
   String  eventType = " ";

   public  ShowEvents( int  WidthInPixels, int heightInPixels )
      {
      setTitle( "Show Events" );
      resize( WidthInPixels, heightInPixels );
      }

   public boolean handleEvent( Event userAction )
      {
      if ( userAction.id == Event.WINDOW_DESTROY )
         displayMessage( "WINDOW_DESTROY" );
      else if ( userAction.id == Event.MOUSE_DOWN )
         displayMessage( "MOUSE_DOWN" );
      else if ( userAction.id == Event.MOUSE_ENTER )
         displayMessage( "MOUSE_ENTER" );
      else if ( userAction.id == Event.MOUSE_EXIT )
         displayMessage( "MOUSE_EXIT" );
      return super.handleEvent( userAction );
      }

   public void displayMessage( String message)
      {
      System.out.println( message );
      eventType  =  message;
      repaint();               // redraw the window
      }

   public  void  paint(  Graphics  display  )
      {
      display.drawString(  eventType , 30, 40  );
      }

   public  static  void  main( String  args[] ){
      ShowEvents  mainWindow = new  ShowEvents( 300,  200 );
      mainWindow.show();
      }
   }
Doc 21, AWT Basics Slide # 11

Output

Comments
To redraw the screen, call repaint()

repaint will call paint

Do not call paint directly

System.out.println( message ) was called for debugging
and to show history, not normally done

   public void displayMessage( String message)
      {
      System.out.println( message );
      eventType  =  message;
      repaint();               // redraw the window
      }

Doc 21, AWT Basics Slide # 12

Showing All Events
The following program will show all events that are sent to the window

You will not be able to generate all events at this time!

Have fun

import  java.awt.*;

class  ShowEvents  extends  Frame 
   {
   String  eventType = " ";

   public  ShowEvents( int  WidthInPixels, int heightInPixels )
      {
      setTitle( "Show All Events" );
      resize( WidthInPixels, heightInPixels );
      }

   public boolean handleEvent( Event userAction )
      {
      if ( userAction.id == Event.ACTION_EVENT ) 
         displayMessage( "ACTION_EVENT" );
      else if ( userAction.id == Event.DOWN ) 
         displayMessage( "DOWN" );
      else if ( userAction.id == Event.GOT_FOCUS ) 
         displayMessage( "GOT_FOCUS" );
      else if ( userAction.id == Event.KEY_ACTION ) 
         displayMessage( "KEY_ACTION" );
      else if ( userAction.id == Event.KEY_ACTION_RELEASE ) 
         displayMessage( "KEY_ACTION_RELEASE" );
      else if ( userAction.id == Event.KEY_PRESS ) 
         displayMessage( "KEY_PRESS" );
      else if ( userAction.id == Event.KEY_RELEASE ) 
         displayMessage( "KEY_RELEASE" );
      else if ( userAction.id == Event.LEFT ) 
         displayMessage( "LEFT" );
      else if ( userAction.id == Event.LIST_DESELECT ) 
         displayMessage( "LIST_DESELECT" );
      else if ( userAction.id == Event.LIST_SELECT ) 
         displayMessage( "LIST_SELECT" );
      else if ( userAction.id == Event.LOAD_FILE ) 
         displayMessage( "LOAD_FILE" );
      else if ( userAction.id == Event.LOST_FOCUS ) 
         displayMessage( "LOST_FOCUS" );

Doc 21, AWT Basics Slide # 13

      else if ( userAction.id == Event.MOUSE_DOWN ) 
         displayMessage( "MOUSE_DOWN" );
      else if ( userAction.id == Event.MOUSE_DRAG ) 
         displayMessage( "MOUSE_DRAG" );
      else if ( userAction.id == Event.MOUSE_ENTER ) 
         displayMessage( "MOUSE_ENTER" );
      else if ( userAction.id == Event.MOUSE_EXIT ) 
         displayMessage( "MOUSE_EXIT" );
      else if ( userAction.id == Event.MOUSE_MOVE ) 
         displayMessage( "MOUSE_MOVE" );
      else if ( userAction.id == Event.MOUSE_UP ) 
         displayMessage( "MOUSE_UP" );
      else if ( userAction.id == Event.SAVE_FILE ) 
         displayMessage( "SAVE_FILE" );
      else if ( userAction.id == Event.SCROLL_ABSOLUTE ) 
         displayMessage( "SCROLL_ABSOLUTE" );
      else if ( userAction.id == Event.SCROLL_LINE_DOWN ) 
         displayMessage( "SCROLL_LINE_DOWN" );
      else if ( userAction.id == Event.SCROLL_LINE_UP ) 
         displayMessage( "SCROLL_LINE_UP" );
      else if ( userAction.id == Event.SCROLL_PAGE_DOWN ) 
         displayMessage( "SCROLL_PAGE_DOWN" );
      else if ( userAction.id == Event.SCROLL_PAGE_UP ) 
         displayMessage( "SCROLL_PAGE_UP" );
      else if ( userAction.id == Event.WINDOW_DEICONIFY ) 
         displayMessage( "WINDOW_DEICONIFY" );
      else if ( userAction.id == Event.WINDOW_DESTROY ) 
         displayMessage( "WINDOW_DESTROY" );
      else if ( userAction.id == Event.WINDOW_EXPOSE ) 
         displayMessage( "WINDOW_EXPOSE" );
      else if ( userAction.id == Event.WINDOW_ICONIFY ) 
         displayMessage( "WINDOW_ICONIFY" );
      else if ( userAction.id == Event.WINDOW_MOVED ) 
         displayMessage( "WINDOW_MOVED" );
      return super.handleEvent( userAction );
      }

   public void displayMessage( String message)
      {
      System.out.println( message );
      eventType  =  message;
      repaint();               // redraw the window
      }

   public  void  paint(  Graphics  display  )
      {
      display.drawString(  eventType , 30, 40  );
      }

   public  static  void  main( String  args[] ){
      ShowEvents  mainWindow = new  ShowEvents( 300,  200 );
      mainWindow.show();
      }
   }

Doc 21, AWT Basics Slide # 14

Handling Events
There are three different ways in which a window can be notified of events

1) handleEvent

Window has a handleEvent method which is sent all events

The handleEvent picks the events it is interested in them and handles the event

2) Special convenience methods handle a specific event

action( Event, Object )	mouseEnter( Event, x, y )
keyDown( Event, int key )	mouseExit( Event, x, y )
keyUp( Event, int key )	mouseMove( Event, x, y )
mouseDown( Event, x, y )	mouseUp( Event, x, y )
mouseDrag( Event, x, y )

3) Button and menu can handle events

Doc 21, AWT Basics Slide # 15

Using Convenience Event Methods


import  java.awt.*;

class  EventMethods  extends  Frame {
   String  eventMessage = " ";

   public  EventMethods( int  WidthInPixels, int heightInPixels ) {
      setTitle( "Event Methods" );
      resize( WidthInPixels, heightInPixels );
      show();
   }

   public boolean mouseDown( Event userAction, int x, int y ) {
      displayMessage("click!... " + x + " " + y);
      return true;
   }

   public boolean keyDown( Event userAction, int key )  {
      displayMessage(  "Key pressed!... " + key );
      return true;
   }

   public void displayMessage( String message )  {
      System.out.println( message );
      eventMessage  =  message;
      repaint();               // redraw the window
   }

   public  void  paint(  Graphics  display  )  {
      display.drawString(  eventMessage , 30, 40  );
   }

   public  static  void  main( String  args[] ){
      EventMethods  mainWindow;
      mainWindow  =  new  EventMethods( 300,  200 );
      }
   }
Doc 21, AWT Basics Slide # 16

Output

Doc 21, AWT Basics Slide # 17

Return, handleEvent, Convenience methods
If you completely handle an event then return true

In handleEvent if you do not handle or completely handle an event then return super.handleEvent( userAction );

   public boolean handleEvent( Event userAction )
      {
      if ( userAction.id == Event.MOUSE_DOWN )
         {
         displayMessage( "MOUSE_DOWN" );
         return true;
         }
      else if ( userAction.id == Event.MOUSE_ENTER )
         displayMessage( "MOUSE_ENTER" );

      return super.handleEvent( userAction );
      }

In convenience method if you do not handle or completely handle an event then return false

Do NOT return super.handleEvent in convenience method

   public boolean mouseDown( Event userAction, int x, int y ) {
      displayMessage("Mouse down" + x + " " + y);
      return true;
   }

   public boolean mouseEnter( Event userAction, int x, int y ) {
      displayMessage("Mouse Enter" + x + " " + y);
      return false;
   }
Doc 21, AWT Basics Slide # 18

How do handleEvent and Event Methods Work?

import  java.awt.*;

class  EventMethods  extends  Frame {

   public  EventMethods( int  WidthInPixels, int heightInPixels ) {
      setTitle( "Event Methods" );
      resize( WidthInPixels, heightInPixels );
      show();
   }

   public boolean handleEvent( Event userAction ){
      if ( userAction.id == Event.MOUSE_DOWN  )
         displayMessage( "Mouse down in handle Event" );
      return  super.handleEvent( userAction );
      }

   public boolean mouseDown( Event userAction, int x, int y ) {
      displayMessage( "Mouse down in mouse down");
      return false;
   }

   public void displayMessage( String message )  {
      System.out.println( message );
   }

   public  void  paint(  Graphics  display  )  {
      display.drawString(  "Constant" , 30, 40  );
   }

   public  static  void  main( String  args[] ){
      EventMethods  mainWindow;
      mainWindow  =  new  EventMethods( 300,  200 );
   }
}

Output Mouse down in handle Event
Mouse down in mouse down

Doc 21, AWT Basics Slide # 19

How do handleEvent and Event Methods Work?
First handleEvent is sent to the window

If your class has handleEvent it is run

If not the default handleEvent is run

super.handleEvent is the default handleEvent

The default handleEvent will call mouseDown, etc.

If your class has mouseDown it is then run

If your class does not have mouseDown the default mouseDown is run

The default mouseDown does nothing

The default methods are in java.awt.Component

Doc 21, AWT Basics Slide # 20

Graphics

The paint method has a graphics object as an argument

   public  void  paint(  Graphics  display  )  {
      display.drawString(  "Constant" , 30, 40  );
   }

The graphics class contains methods for drawing
Graphics Methods

clearRect(int, int, int, int)	drawString(String, int, int)
clipRect(int, int, int, int)	fill3DRect(int, int, int, int, boolean)
copyArea(int, int, int, int, int, int)	fillArc(int, int, int, int, int, int)
create()	fillOval(int, int, int, int)
create(int, int, int, int)	fillPolygon(int[], int[], int)
dispose()	fillPolygon(Polygon)
draw3DRect(int, int, int, int, boolean)	fillRect(int, int, int, int)
drawArc(int, int, int, int, int, int)	fillRoundRect(int, int, int, int, int, int)
drawBytes(byte[], int, int, int, int)	finalize()
drawChars(char[], int, int, int, int)	getClipRect()
drawImage(Image, int, int, Color, ImageObserver)	getColor()
drawImage(Image, int, int, ImageObserver)	getFont()
drawImage(Image, int, int, int, int, Color, ImageObserver)	getFontMetrics()
drawImage(Image, int, int, int, int, ImageObserver)	getFontMetrics(Font)
drawLine(int, int, int, int)	setColor(Color)
drawOval(int, int, int, int)	setFont(Font)
drawPolygon(int[], int[], int)	setPaintMode()
drawPolygon(Polygon)	setXORMode(Color)
drawRect(int, int, int, int)	toString()
drawRoundRect(int, int, int, int, int, int)	translate(int, int)

Doc 21, AWT Basics Slide # 21

Drawing

import  java.awt.*;

class  Drawing  extends  Frame {

   public  Drawing  ( int  WidthInPixels, int heightInPixels ) {
      setTitle( "Drawing" );
      resize( WidthInPixels, heightInPixels );
      setBackground( Color.green);
      show();
   }

   public  void  paint(  Graphics  display  )  {
      display.setColor( Color.darkGray );

      int x = 50;      int y = 30;
      int width = 40;      int height =  20;
      display.drawOval(  x,  y,  width,  height  );

      x = 100;
      display.drawRect(  x,  y,  width,  height  );

      x = 150;
      display.fillRect(  x,  y,  width,  height  );

      x = 200;
      boolean  raised = true;
      display.draw3DRect(  x,  y,  width,  height,  raised  );
   }

   public  static  void  main( String  args[] ){
      Drawing  mainWindow;
      mainWindow  =  new  Drawing( 300,  200 );
      }
   }

Doc 21, AWT Basics Slide # 22

Output

Doc 21, AWT Basics Slide # 23

Color Predefined Colors in Color Class

black	green	pink
blue	lightGray	red
cyan	magenta	white
darkGray	orange	yellow
gray

Constructors
Color(float, float, float)

Creates a color with the specified red, green, and blue values in the range (0.0 - 1.0).

Color(int)

Creates a color with the specified combined RGB value consisting of the red component in bits 16-23, the green component in bits 8-15, and the blue component in bits 0-7.

Color(int, int, int)

Creates a color with the specified red, green, and blue values in the range (0 - 255).

Methods

Doc 21, AWT Basics Slide # 24

brighter()	getHSBColor(float,float,float)
darker()	getRed()
equals(Object)	getRGB()
getBlue()	hashCode()
getColor(String)	HSBtoRGB(float,float,float)
getColor(String,Color)	RGBtoHSB(int,int,int,float[])
getColor(String,int)	toString()
getGreen()

Drawing Modes
Normal paint mode is to cover bits as you draw

In normal draw mode a red line on a red area you will not see the line

In XOR mode colors are toggled

There is a current drawing color and an XOR color

If you draw over an area that is already in the current drawing color, the XOR color is used

Change to XOR mode with Graphics method

setXORMode( Color XORColor )

Change to paint mode with Graphics method

setPaintMode()

Doc 21, AWT Basics Slide # 25

Fonts

import  java.awt.*;
class  FancyHello  extends  Frame  {
   public  FancyHello()
      {
      int  pointSize  =  24;
      setFont( new Font( "TimesRoman", Font.BOLD, pointSize ));

      setBackground( Color.black );
      setTitle( "Hi Mom" );

      resize( 150,  150);
      show();
      }

   public  void  paint(  Graphics  display  )
      {
      int x  =  50;
      int y  =  60;
      display.setColor( Color.white );
      display.drawString(  "Hello", x, y );
      display.setFont( new Font("Courier", Font.ITALIC, 12 ));

      x  =  50;
      y  =  100;
      display.drawString(  "World", x, y );
      }

   public  static  void  main( String  args[] )
      {
      new  FancyHello();
      }
   }
Doc 21, AWT Basics Slide # 26

Output

Doc 21, AWT Basics Slide # 27

Font Issues What Fonts are Available?

import  java.awt.Toolkit;
class  WhatFonts {
   public  static  void  main( String  args[] )
      {
      Toolkit  platformInfo = Toolkit.getDefaultToolkit();
      String[] availbleFonts = platformInfo.getFontList();
      for ( int index = 0; index < availbleFonts.length; index++ )
         System.out.println( availbleFonts[ index ]  );
      }
   }

Standard? Answer Dialog
Helvetica
TimesRoman
Courier
Symbol

What Font Styles are Available?
Font.PLAIN
Font.BOLD
Font.ITALIC

These can be mixed

 new Font("Courier", Font.ITALIC + Font.BOLD, 12 )
Doc 21, AWT Basics Slide # 28

Font Issues How many pixels in a string?
Use FontMetrics to find the answer

import  java.awt.*;
class  TextSize  extends  Frame  
   {
   public  TextSize()
      {
      setTitle( "Text Size" );
      resize( 300,  200);
      show();
      }

   public  void  paint(  Graphics  display  )
      {
      Font largeText = new Font( "TimesRoman", Font.BOLD, 24 );
      FontMetrics  largeTextSize;
      largeTextSize = display.getFontMetrics( largeText );

      display.setFont( largeText  );
      display.setColor( Color.black );

      int x  =  50;
      int y  =  90;
      display.drawString(  "Hello ", x, y );

      x = x + largeTextSize.stringWidth( "Hello " );
      display.drawString(  "World", x, y );
      }

   public  static  void  main( String  args[] )
      {
      new  TextSize();
      }
   }

Doc 21, AWT Basics Slide # 29

Output

Doc 21, AWT Basics Slide # 30

Cursors

Types of Cursors

CROSSHAIR_CURSOR	NW_RESIZE_CURSOR
DEFAULT_CURSOR	S_RESIZE_CURSOR
E_RESIZE_CURSOR	SE_RESIZE_CURSOR
HAND_CURSOR	SW_RESIZE_CURSOR
MOVE_CURSOR	TEXT_CURSOR
N_RESIZE_CURSOR	W_RESIZE_CURSOR
NE_RESIZE_CURSOR	WAIT_CURSOR

These are defined in java.awt.Frame

The setCursor method in Frame changes the mouse Cursor

Doc 21, AWT Basics Slide # 31

Cursor Example

class  Cursors  extends  Frame {
   public  Cursors( int  WidthInPixels, int heightInPixels ) {
      setTitle( "Cursors" );
      resize( WidthInPixels, heightInPixels );
      show();
   }

   public boolean mouseDown( Event userAction, int x, int y ) {
      setCursor( Frame.HAND_CURSOR );
      return true;
   }

   public boolean mouseUp( Event userAction, int x, int y ) {
      try {
         long millisecondDelay = 500;
         setCursor( Frame.WAIT_CURSOR );
         Thread.sleep( millisecondDelay );
         setCursor( Frame.TEXT_CURSOR );
         Thread.sleep( millisecondDelay );
         setCursor( Frame.MOVE_CURSOR );
         Thread.sleep( millisecondDelay );
         setCursor( Frame.DEFAULT_CURSOR );
         }
      catch ( InterruptedException interrupt )  { }
      return true;
   }

   public  void  paint(  Graphics  display  )  {
      display.drawString(  "Cursors" , 30, 40  );
   }

   public  static  void  main( String  args[] ){
      Cursors  mainWindow  =  new  Cursors( 300,  200 );
      mainWindow.setCursor( Frame.WAIT_CURSOR );
      }
   }

Doc 21, AWT Basics Slide # 32

Frame Public Variables

CROSSHAIR_CURSOR	NW_RESIZE_CURSOR
DEFAULT_CURSOR	S_RESIZE_CURSOR
E_RESIZE_CURSOR	SE_RESIZE_CURSOR
HAND_CURSOR	SW_RESIZE_CURSOR
MOVE_CURSOR	TEXT_CURSOR
N_RESIZE_CURSOR	W_RESIZE_CURSOR
NE_RESIZE_CURSOR	WAIT_CURSOR

Frame Methods

addNotify()	paramString()
dispose()	remove(MenuComponent)
getCursorType()	setCursor(int)
getIconImage()	setIconImage(Image)
getMenuBar()	setMenuBar(MenuBar)
getTitle()	setResizable(boolean)
isResizable()	setTitle(String)

CS535 Object-Oriented Programming & Design Fall Semester, 1996 Doc 21, AWT Basics

Contents of Doc 21, AWT Basics

CS535 Object-Oriented Programming & Design
Fall Semester, 1996
Doc 21, AWT Basics