Objects First With Java - Chapter 8

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GUI: Graphical User Interface

AWT/SWING:

Components

Drag and Drop in NetBeans

Events

Listeners

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Components

•
GUIs are build using standard
components, for instance:

–
Windows (Frames in Java)

–
Menu bars

–
Text fields

–
List boxes

–
Buttons

–
Etc.

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Java.awt and javax.swing

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Some
AWT
and

Swing
Classes

java.lang.Object

java.awt.Component

java.awt.Container

javax.swing.JComponent

java.awt.Window

java.awt.Frame

javax.swing.JFrame

javax.swing.JLabel

javax.swing.JToolbar

javax.swing.JPopupMenu

javax.swing.JFileChooser

javax.swing.JPanel

Note the use
of inheritance

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Graphical User Interfaces

•
A Graphical User Interface (GUI) is created
with at least three kinds of objects

–
components

–
events

–
Listeners

•
Java standard class library provides these
objects for us

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Components and Containers

•
A GUI
component

defines a screen
element to display information or allow the
user to interact with the program

–
buttons, text fields, labels, menus, etc.

•
A
container

is a special component that
holds and organizes other components

–
dialog boxes, applets, frames, panels, etc.


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Hello World Example

import javax.swing.*;

public class HelloWorldSwing {


public static void main(String[] args) {



JFrame frame = new JFrame("HelloWorldSwing");



JLabel label = new JLabel("Hello World");




frame.getContentPane().add(label);



frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);



frame.setSize(200,200);



frame.setVisible(true);


}

}


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Frame

•
The main component is a frame.

•
Frame is the Java term for what is generally called a
‘window’.

•
In Swing frames are realised by the class
JFrame

•
A frame is a rectangular area:

–
title bar at the top

–
The title bar contains buttons for closing, maximizing and
minimizing of the frame

–
Below the title bare is an area at which further graphical
components can be placed

–
This area is divided into two parts:

•
space for a menu bar at the upper edge

•
content pane below

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Elements of a JFrame

Title

Menu bar

Content pane

Window controls

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import java.awt.*;

import javax.swing.*;


public class FirstFrame extends JFrame

{




public FirstFrame()


{



super("My First Frame");



setSize(200,200);



setVisible(true);


}

}

Import

libraries

Inherit

JFrame

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import java.awt.*;

import javax.swing.*;

public class SecondFrame extends JFrame{


//Components neede to build the menubar


private JMenuBar menuBar;


private JMenu fileMenu, editMenu;


private JMenuItem openItem, quitItem;


public SecondFrame() {


super("My Second Frame");


buildMenu();


setSize(200,200);


setVisible(true);


}


private void buildMenu(){


menuBar = new JMenuBar();


fileMenu = new JMenu("File");


editMenu = new JMenu("Edit");


menuBar.add(fileMenu);


menuBar.add(editMenu);


openItem = new JMenuItem("Open");


quitItem = new JMenuItem("Quit");


fileMenu.add(openItem);


fileMenu.add(quitItem);


this.setJMenuBar(menuBar);


}

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private void buildInputpart(){


panelIO = new JPanel();


panelIO.setLayout(null);


labFirstName = new JLabel("First Name:");


labLastName = new JLabel("Last Name: ");


txtFirstName = new JTextField();


txtFirstName.setToolTipText("Input first name");


txtLastName = new JTextField();


txtLastName.setToolTipText("Input last name");


addComponent(panelIO, labFirstName, 20,20,70,20);


addComponent(panelIO, txtFirstName, 100,20,150,20);


addComponent(panelIO, labLastName, 20,45,70,20);


addComponent(panelIO, txtLastName, 100,45,150,20);


this.add(panelIO);

}


private void buildButtonpart(){


panelButton = new JPanel();


panelButton.setLayout(null);


submitBut = new JButton("Submit");


clearBut = new JButton("Clear");


addComponent(panelButton, submitBut, 20,80, 100,20);


addComponent(panelButton, clearBut, 130,80, 100,20);


this.add(panelButton);


}


private void addComponent(Container container,


Component c,int x,int y,int width,int height){


c.setBounds(x,y,width, height);


container.add(c);


}

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This is unbearable!

•
Instead an IDE supporting Drag and Drop


•
For instance NetBeans:

GUI Building in NetBeans IDE 5.0

or

http://www.netbeans.org/kb/55/quickstart
-
gui.html



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Creating a GUI Project

1.
Choose File > New Project. Alternately, you can click the New Project icon
in the IDE toolbar.


2.
In the Categories pane, select the General node and in the Projects pane,
choose Java Application. Click Next.


3.
Enter ContactEditor in the Project Name field and specify the project
location.


4.
Ensure that the Set as Main Project checkbox is selected and deselect
Create Main Class if it is selected.


5.
Click Finish.

The IDE creates the
ContactEditor

folder on your system in the designated
location. This folder contains all of the project's associated files, including its
Ant script, folders for storing sources and tests, and a folder for project
-
specific metadata. To view the project structure, use the IDE's Files window.


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Adding a Main Component

To create a JFrame container:

1.
In the Projects window, right
-
click the ContactEditor node and
choose New > JFrame Form.


2.
Enter ContactEditorUI as the Class Name.


3.
Enter
my.contacteditor

as the package.


4.
Click Finish. The IDE creates the

ContactEditorUI
form and the
ContactEditorUI
class within the
ContactEditorUI.java
application
and opens the
ContactEditorUI
form in the GUI Builder. Notice that
the
my.contacteditor package replaces the default package.


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Event Driven

•
Programs with graphical user interfaces (GUIs)
are event driven:

–
the program reacts to actions of the user

–
these actions generate (‘fire’) events

–
examples of events are:

•
pressing a key

•
moving the mouse

•
clicking on a button

•
selecting a menu item

–
Components that reacts to events are called
Listeners

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Eventhandling

User interface

GUI Components fires the event


in response to being clicked

Listener

React to the events

Java code

Components


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Hello World
–


now with buttons!


private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {


jTextField1.setText("Hello World!");


}



private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {


System.exit(0);


}



jButton1.setText("Say Hello");


jButton1.addActionListener(new java.awt.event.ActionListener() {


public void actionPerformed(java.awt.event.ActionEvent evt) {


jButton1ActionPerformed(evt);


}


});

Listener
generated by
NetBeans


Called when the
event occurs

We write the body of
the event handler


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Do it!

The tutorial:
Adding Functionality to Buttons: A Beginners Guide