Download java_pres1.ppt

Java and AWT
CPS 470 Spring 1998
Laura Campbell
1
Java 1.0
• ADM group thinks they can do
it using 1.0 instead of 1.1
• Better chance of running under
Netscape than 1.1
• /usr/java/bin/javac
• /usr/java/bin/appletviewer
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Setup for Java on SGIs
• Add to .personal file:
if (`uname` == "IRIX") then
set path=($path /usr/java/bin)
endif
• A path to the correct javac
(/opt/bin/javac) should already
be set up on the Suns.
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Java.awt-components
• MenuComponent
– MenuBar
– MenuItem
• Menu, CheckboxMenuItem
• Component
– Button, Canvas, Checkbox,
Choice, Label, List, Scrollbar
– TextComponent
• TextArea, TextField
– Container
• Panel, Window
4
References
• URLs on class web page(s)
• Java books on reserve in
Engineering Library
• SunSoft Press Java Series
• Java API (James Gosling, et al)
5
Lab Assignment
• Files
– MsuMap.java
– MyCanvas.java
– ?.java (you’ll subclass Choice)
• Task
– Keep the map display and the
choice items synchronized
• How
– Subclass Choice so you can
override the event handling
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// MsuMap.java
import java.awt.*;
import java.applet.*;
import java.net.*;
public class MsuMap extends Canvas {
private Image im;
private Image msumap;
private Image selectedMsumap;
public MsuMap(Image i1, Image i2) {
msumap = i1;
selectedMsumap = i2;
im = msumap;
}
public void paint( Graphics g ) {
g.drawImage(im,0,0,this);
}
public boolean handleEvent( Event event ) {
Object target = event.target;
int id = event.id;
if ((target == this) && (id == Event.MOUSE_DOWN)) {
if (im == msumap) {
im = selectedMsumap;
}
else {
im = msumap;
}
repaint();
return true;
}
return false;
}
}
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// MyCanvas.java (original)
import java.applet.*;
import java.awt.*;
import java.net.*;
public class MyCanvas extends Applet {
java.awt.Component canvas;
java.awt.Choice choiceBox; // Initialize this object.
public void init() {
super.init();
URL codebase = getCodeBase();
Image msumap = getImage(codebase, "msumap.gif");
Image selected = getImage(codebase, "selected.gif");
// Manual layout may be used for appletviewer
// but should NOT be used for Netscape (it gets confused).
// Set the layout to null to override it with manual commands.
//
// setLayout(null); // may uncomment this line for appletviewer
// Set the background color to off-white.
setBackground(new Color(0xfaf0e6));
resize(800, 500);
add(canvas = new MsuMap(msumap,selected));
canvas.move(43, 20);
canvas.resize(600, 500);
canvas.show();
add(choiceBox = new java.awt.Choice());
choiceBox.addItem("Route");
choiceBox.addItem("Facility");
choiceBox.setFont(new Font("Dialog", 0, 12));
// may uncomment the next line if manual layout used for appletviewer
// choiceBox.move(650, 49);
choiceBox.show();
}
}
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// MyCanvas.java (revised)
import java.applet.*;
import java.awt.*;
import java.net.*;
public class MyCanvas extends Applet {
java.awt.Component canvas;
RorF_Choice choiceBox; // Using our own subclassed Choice
public void init() {
super.init();
URL codebase = getCodeBase();
Image msumap = getImage(codebase, "msumap.gif");
Image selected = getImage(codebase, "selected.gif");
// Manual layout may be used for appletviewer
// but should NOT be used for Netscape (it gets confused).
// Set the layout to null to override it with manual commands.
//
// setLayout(null); // may uncomment this line for appletviewer
// Set the background color to off-white.
setBackground(new Color(0xfaf0e6));
resize(800, 500);
add(canvas = new MsuMap(msumap,selected));
canvas.move(43, 20);
canvas.resize(600, 500);
canvas.show();
add(choiceBox = new RorF_Choice()); // Use our own
// removed lines of code were placed in the RorF_Choice constructor
// may uncomment the next line if manual layout used for appletviewer
// choiceBox.move(650, 49);
choiceBox.show();
}
}
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// RorF_Choice.java (subclasses Choice)
import java.applet.*;
import java.awt.*;
import java.net.*;
public class RorF_Choice extends Choice {
public RorF_Choice() {
// call parent’s constructor first
super();
// place the 3 lines of code from MyCanvas.java here
// (use the implicit object “this” instead of “choiceBox”)
}
public boolean action( Event event, Object obj) {
// cast the object argument to a String
// print out the event and string now showing on menu
System.out.println(“\nPut some message here.”);
// return true if event handled successfully
// return false if event should be passed to parent
return super.action(event,obj);
}
}
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