Applets and Frames

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 2 Applets Usually graphical in content One way of writing Java programs (besides applications) Java programs that can be embedded in HTML documents (web pages) Note: Not all web browsers automatically support Java 2. You will have to install the Java Plug-in, which is done automatically if you installed Java on your machines.

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 3 JApplet This is the “swing” version of Applets JApplet is the newer version of the Applet class that is used with Java’s swing GUI components We will be using this in class

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 4 Java Applet classes Abstract Window Toolkit (AWT) Contain classes that provide the Java graphical user interface (GUI) components Java Foundation Classes Was an extension to java Contains swing components written entirely in java

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 5 Writing Java Applets import javax.swing.*; import java.awt.*; /**This applet displays “Hello, world!” on a label.**/ public class MyApplet extends JApplet { private JLabel helloLabel; public void init() { Container c = getContentPane(); c.setLayout( new FlowLayout() ); this.helloLabel = new JLabel( "Hello, world!" ); c.add( helloLabel ); }

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 6 Running Java Applets Recall that an.html needs to be created to execute applets Executing through an IDE In BlueJ:, right-click on the class and select “Run Applet”, then Click on “OK” and wait for the applet to appear In JCreator, create the.html file and execute that file Executing through the Command Prompt appletviewer file.html Executing through a browser: Go to the folder where the.html and the.class resides Double-click on that and wait for the browser to load

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 7 Writing Web Pages with Applets You will have to include this in the body of the HTML file to tell it you are embedding an applet: To embed the class file of MyApplet.java:

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 8 Container and getContentPane() Container A generic AWT container a component that can contain other AWT components Most important methods: setLayout() and add() getContentPane() A method found in JApplet This method returns the contentPane object (a Container) for this applet. You’ll need these to be able to add components to your applet.

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 9 public void init() Every applet must implement one or more of the init(), start(), and paint() methods. This is what a browser usually looks for when it runs applets. You will have to include the init() method to give your applet its intended appearance and functionality Think of init() as a constructor for your applet This is where you add the components to a container The applet is in effect an aggregate class containing the labels, buttons, text fields, and other visual components

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 10 Importing packages To be able to use JApplet and swing components you will have to import the javax.swing package and to be able to use some AWT components, you will have to import the java.awt package. At the top of your java class: import javax.swing.*; import java.awt.*;

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 11 The Java Swing Components Java’s framework for programming lightweight GUI Components Lightweight here means that it’s written in and it runs entirely in Java Components JButton, JTextField, JTextArea, JLabel, JPanel Others (self-study) You will have to add these components to an AWT container

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 12 The Java Abstract Window Toolkit (AWT) Java’s framework for programming Graphical User Interfaces (GUIs) Containers Layout Managers FlowLayout, GridLayout, BorderLayout CardLayout, GridBagLayout (self-study)

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 13 Components JButton: clickable visual object JLabel: text JTextField contains editable text methods setText() and getText() JTextArea same as JTextField but can support multiple lines JPanel may contain other visual components methods setLayout() and add()

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 14 Layout Managers FlowLayout objects are placed row by row, left to right GridLayout divides container into an m by n grid BorderLayout divides container into 5 parts Center, North, South, East, West e.g., add( component, “North” ); See examples

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 15 Panel A Panel is a component that can contain other objects We can do more complex layouts by using Panels within the Applet or even Panels within Panels

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 16 Designing a GUI for an Applet import java.awt.*; import javax.swing.*; extends JApplet inherits built-in features of JApplet Declare variables for the different visual components to be placed on the applet In init() method, create visual components (use new) establish layout manager (use setLayout()) default for JApplets: BorderLayout add visual components (use MyContainer.add()) nested layouts possible (use Panels)

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 17 Applet Example import javax.swing.*; import java.awt.*; public class HelloWorldApplet extends JApplet { private JButton button; private JTextField textField; private JLabel label; public void init() { Container c = getContentPane(); c.setLayout( new FlowLayout() ); label = new JLabel( "Hello, World!" ); c.add( label ); textField = new JTextField( "Enter your name here", 15 ); c.add( textField ); button = new JButton( "Click Me" ); c.add( button ); }... }

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 18 HTML file for the applet <applet code=HelloWorldApplet.class width=300 height=200>

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 19 JFrame Use JFrame instead of JApplet if you want a GUI application (instead of a web-based applet) Extend JFrame instead of JApplet Instead of the init() method, place initialization code in the class’ constructor Need a main method (perhaps in a separate class) that instantiates and displays the frame

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 20 Frame example import javax.swing.*; import java.awt.*; public class HelloWorldFrame extends JFrame { private JButton button; private JTextField textField; private JLabel label; public HelloWorldFrame() { Container c = this.getContentPane(); c.setLayout( new FlowLayout() ); label = new JLabel( "Hello, World!" ); c.add( label ); textField = new JTextField( "Enter your name here", 15 ); c.add( textField ); button = new JButton( "Click Me" ); c.add( button ); }... }

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 21 Driver class for the frame import javax.swing.*; public class FrameRunner { public static void main( String args[] ) { JFrame f = new HelloWorldFrame(); f.setSize( 200, 300 ); f.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); f.setVisible( true ); }

Copyright 2005, by the authors of these slides, and Ateneo de Manila University. All rights reserved L14: GUI Slide 22 About frames When using frames, you could call setLayout() and add() directly on the frame object No need to declare a Container object or call getContentPane() Other methods applicable on a frame object (these can be called in the frame’s constructor, or from the driver) setSize(): sets the dimensions of the frame setTitle(): sets the title bar of the frame