Transcript using Textpad & Eclipse

Using Textpad, &Eclipse & a
little Java, too
Creating simple Java applications
and applets with Textpad or
Eclipse
About the programs
• Eclipse is open source, Textpad is
shareware. Eclipse can be downloaded
from http://www.eclipse.org/. Textpad is
available from Helios.com.
• Instead, you can use any editor, but save
java files as text files with the .java
extension.
• Eclipse and Textpad should be available in
the campus labs.
Eclipse
• If you download, be
sure to download a
java version (not C++)
of Eclipse.
• When you start up,
select a workspace
folder.
• Eclipse does come
with its own tutorials
and exercises.
Create a project
• Select:
– New
– Project
– java project
– give it a name
– finish
• Depending on your eclipse version, it may
not look precisely like my screenshots
New project
Aside: Java projects
• Java projects are comprised of packages,
classes and interfaces.
• When building a project, you can name
packages or use the “default package”.
• Packages are like namespaces. They help
avoid naming collisions and indicate a required
directory structure. The package
mystuff.utilities.file_utilities is in the directory
proj_name\mystuff\utilities\file_utilities
• Interfaces contain a set of method signatures.
Classes implementing an interface must define
these methods.
Eclipse screenshot: a java class in the
default package, some minimal content,
selecting Run/run as application
Application to open a frame
(window) on the screen
import javax.swing.*;//JFrame definition is in here
public class Application {
public static void main(String args[]){
System.out.println("hello");
doStuff();//a method call
}
public static void doStuff(){//method definition
JFrame myframe=new JFrame();
myframe.setBounds(10,10,300,400);
myframe.setVisible(true);//a frame with nothing on it
}
}
Revised function doStuff which opens a
window with various widgets on it
public static void doStuff(){
JFrame myframe=new JFrame();
myframe.setBounds(10,10,300,400);
JPanel mypanel=new JPanel();
JTextField a,b;
JLabel label=new JLabel("answer will
appear here");
JButton button=new JButton("press me");
a=new JTextField(20);
b=new JTextField(20);
mypanel.add(a);
mypanel.add(b);
mypanel.add(button);
mypanel.add(label);
myframe.add(mypanel,BorderLayout.CEN
TER);
myframe.setVisible(true);
}
Adding functionality
• The “button” has to listen for a click on it and
then we should probably get the input values
and do something.
• There are many ways to add this functionality to
our application. One way, is to let the outer
class implement the ActionListener interface, so
that it will be responsible for indicating what
should happen when a button click occurs. This
responsibility could fall to any class which
implements the ActionListener interface.
• See next slide for this second possibility.
A minimal solution
class MyListener implements
ActionListener {
@Override
public void actionPerformed(ActionEvent e)
{
//put code here later
}
}
Next…
• Add the ActionListener to the button.
Then, when the button is pressed (in
actionPerformed method), get input
values, do something with them and
display the result.
• I’ve moved the declarations “up” to the
Applications “global” area. See code in
slide notes later.
Running our application
Eclipse project…application’s
constructor… entire app in slide notes
public Application(){
super();
System.out.println("start constructor");//trace line… could be handled by logging
JFrame myframe=new JFrame();
myframe.setBounds(10,10,300,400);
mypanel=new JPanel();
MyListener mylistener=new MyListener();
label=new JLabel("answer will appear here");
JButton button=new JButton("press me");
a=new JTextField(20);
b=new JTextField(20);
mypanel.add(a);
mypanel.add(b);
mypanel.add(button);
mypanel.add(label);
button.addActionListener(mylistener);
myframe.add(mypanel,BorderLayout.CENTER);
myframe.setVisible(true);
System.out.println("end constructor"); //trace line… could be handled by logging
}
Textpad…same code
• You will need to slightly
configure your own
version of Textpad,
adding javac command
to tools if you wish to
compile from within
Textpad
• Run the .class file from
the command line.
• Looks the same.
Aside: Command line on blackscreen
DOS
• You can run projects from within Eclipse. If you add tools and set
preferences in Textpad, you can run projects in Textpad, too.
• To run in DOS:
• Path settings must contain paths to executables. Classpaths must
contain paths to classes to be executed. These can be set –
depending on your O.S. - in control panel/environment variables.
• To set a classpath you might type something like
– set CLASSPATH=
.;C:\jarfiles\ejb.jar;C:\jarfiles\jndi.jar;C:\jarfiles\persistence.jar;C:\ejbjarfile
s\j2ee.jar;C:\myproject\src;
• Assuming classpaths are properly set you compile a class named
myclass.java with the command:
– C:\myproject\src>javac myclass.java
• Assuming classpaths are properly set you run a class named
myclass.class with the command:
– C:\myproject\src>java myclass
About applets
• An applet is an internet program. You would
“access” it, by entering a url to an html file that
“points” to the class.
• In java, an applet is defined as a special sort of
a panel.
• To run an applet, you must post both the class
file (result of javac command) and the special
html file, on your w drive.
• To access the applet, you enter something like
http://students.oneonta.edu/LastFM99/subdir/myap
plet.html
More about applications and
applets
• Applications usually need a window, a JFrame in
swing terminology. An applet uses the browser
window, so it does not require a special window
to be opened.
• One way to create code which can run either
way, is to put all the functionality into a JPanel.
In the init method, add an instance of this JPanel
to the applet. Supply a main method too, in
case it is run as an application. Here, construct a
JFrame and add the panel to the JFrame.
Simple HTML for an applet
<html>
<applet code="MyApplet.class" width=200
height=300>
</applet>
</html>
A minimal applet with some widgets
on it
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;//JFrame in here
public class AppletEX extends JApplet{
public void init(){//applet’s init method browser will run this
Container c=getContentPane();
JTextField a,b;
JLabel label;
c.setLayout(new FlowLayout());
label=new JLabel("answer will appear here");
JButton button=new JButton("press me");
a=new JTextField(20);
b=new JTextField(20);
c.add(a);
c.add(b);
c.add(button);
c.add(label);
}
}
Running an applet locally
•
Blackscreen commands
c:\Documents and Settings\higgindm\My
Documents>set classpath=.
c:\Documents and Settings\higgindm\My
Documents>appletviewer AppletEX.html
•
AppletEX.HTML file contents
<html>
<applet code="AppletEX.class" width=200
height=300>
</applet>
</html>
A program which can run as either an applet
or application
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;//JFrame in here
public class MyApplet extends JApplet{
public static void main(String args[]){//application’s main method.. Os will run this
JFrame myframe=new JFrame();
MyPanel p=new MyPanel();
myframe.add(p,BorderLayout.CENTER);
myframe.setVisible(true);
myframe.setBounds(100,100,500,500);}
public void init(){//applet’s init method… browser will run this
MyPanel p=new MyPanel();
add(p);
}
static class MyPanel extends JPanel {//put all the functionality in here
JTextField a,b;
JLabel label;
public MyPanel(){
label=new JLabel("answer will appear here");
JButton button=new JButton("press me");
a=new JTextField(20);
b=new JTextField(20);
add(a);
add(b);
add(button);
add(label);
}}}
Running it
• You need to first compile this and be able to access the
.class file generated. I used textpad for this example.
• To view the applet not on the network, but on your
desktop, java comes with a program named
appletviewer.exe. You need to write the html file to
access the applet, even if you are using appletviewer,
(unless you are using a lab machine, in which case you
can execute the applet locally from textpad).
• In comand window, set classpath (example below) then
type
– appletviewer whatever.html
• To run application, type
C:\somepath> set classpath=.
C:\somepath> java classname.class