Section 2: GUIs and Widgets

Input and output is done in applets using widgets.
The code to make widgets are in the library java.awt.*
AWT stands for Abstract windowing toolkit.

Widgets

The most commonly used GUI widgets are:

Labels – an area used for displaying text
Text Field – an area used for input of data or display of output data
Button – an area that can be clicked by the mouse to cause an event

The life-cycle of a widget:

1. Declaration – Conception

Where? Inside the class but outside all of the methods
Example:

JButton exit;
JLabel prompt;
JTextField input;

2. Construction – Birth

Where? Inside init or at the same time you declare it
In the brackets we give the widget an initial label or length
New is the keyword for construction
Example:

exit = new JButton ("Exit");
prompt = new JLabel ("Enter you name");
input = new JTextField (20);

3. Add to the Applet – Leave the hospital

Where? Inside the init method
Example:

add(prompt);
add(exit);
add(input);

4. Do something – Go to school!

Where? Inside the action method (occasionally inside init)
Example:

input.setText("");

The complete code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;


public class littleprog extends Applet implements ActionListener
{
    JLabel prompt;
    JTextField input;
    JButton exit;

    public void init ()
    {
        prompt = new JLabel ("Enter you name");
        input = new JTextField (20);
        exit = new JButton ("Hi");

        exit.setActionCommand ("hi");
        exit.addActionListener (this);
 
        add (prompt);
        add (input);
        add (exit);
    }

    public void actionPerformed (ActionEvent e)
    {
        if ("hi".equals (e.getActionCommand ()))
        {
            prompt.setText ("Hi " + input.getText ());
        }
    }
}

Section 3: Objects

In Java there are two types of things: objects and primitive types.
Primitive types that we know already are int, short, long, float, double, char.
Objects that you know already are: Applets, Color, Button, Label, TextField, Graphic

An object is a set of data and the operations on that data.

1. Example: A Button

It’s Data – font, background colour, foreground colour, label

It’s Operations– setLabel, setBackground, getLabel, setForeground

· To code to make an object is written in a class

· An object’s class has variables to store data and methods to do things to the data.

· To call a method to change a variable in an object, you write:

b1.setLabel(“Click 2X”);
variable-name. Method-name (information needed)

· A Class that makes an object has a special method called a constructor.

· The constructor is used to set up the variables in the class

· The constructor is called like this:

b1 = new Button (“Click Here”);

variable name = new Constructor-name(Information needed)

2. Object Comparison

	Button	Label	TextField
Class name	JButton	JLabel	JTextfield
Variables in it	- font - background colour - foreground colour - label	- font - background colour - foreground colour - text	- font - background colour - foreground colour - text in it
Declare	JButton b1;	JLabel lbl1;	JTextfield txt1;
Constructor	b1 = new JButton("click");	lbl1=new JLabel ("Hi");	txt1=new JTextfield(15);
Other Methods	b1.setBackground(Color.red); b1.setLabel("Hi");	lbl1.setBackground(Color.red); lbl1.setText("Hi");	txt1.setBackground(Color.red); txt1.setText("Hi");
Add to applet	add(b1);	add(lbl1);	add(txt1);