Graphical User Interface (GUI)

Graphical User Interface (GUI)

Application Programming Interface (API): The API provides the core functionality of the Java programming language. It offers a wide array of useful classes ready for use in your own applications.There are two sets of Java APIs for graphics programming: AWT (Abstract Windowing Toolkit) and Swing.

AWT API was introduced in JDK 1.0. Most of the AWT components have become obsolete and should be replaced by newer Swing components.

Swing API, a much more comprehensive set of graphics libraries that enhances the AWT, was introduced as part of Java Foundation Classes (JFC) after the release of JDK 1.1. JFC consists of Swing, Java2D, Accessibility, Internationalization, and Pluggable Look-and-Feel Support APIs. JFC has been integrated into core Java since JDK 1.2.

AWT Packages

AWT is huge! It consists of 12 packages of 370 classes (Swing is even bigger, with 18 packages of 737 classes as of JDK 1.8). Fortunately, only 2 packages - java.awt and java.awt.event - are commonly-used.The java.awt package contains the core AWT graphics classes:

Ø  GUI Component classes, such as Button, TextField, and Label,

Ø  GUI Container classes, such as Frame and Panel,

Ø  Layout managers, such as FlowLayout, BorderLayout and GridLayout,

Ø  Custom graphics classes, such as Graphics, Color and Font.

Ø  The java.awt.event package supports event handling:

Ø  Event classes, such as ActionEvent, MouseEvent, KeyEvent and WindowEvent,

Ø  Event Listener Interfaces, such as ActionListener, MouseListener, KeyListener and WindowListener,

Ø  Event Listener Adapter classes, such as MouseAdapter, KeyAdapter, and WindowAdapter.

AWT provides a platform-independent and device-independent interface to develop graphic programs that runs on all platforms, including Windows, Mac OS, and Unixes.

 Containers and Components

 There are two types of GUI elements:

Ø  Component: Components are elementary GUI entities, such as Button, Label, and TextField.

Ø  Container: Containers, such as Frame and Panel, are used to hold components in a specific layout (such as FlowLayout or GridLayout). A container can also hold sub-containers.

In the above figure, there are three containers: a Frame and two Panels. A Frame is the top-level container of an AWT program. A Frame has a title bar (containing an icon, a title, and the minimize/maximize/close buttons), an optional menu bar and the content display area. A Panel is a rectangular area used to group related GUI components in a certain layout. In the above figure, the top-level Frame contains two Panels. There are five components: a Label (providing description), a TextField (for users to enter text), and three Buttons (for user to trigger certain programmed actions).

GUI components are also called controls (e.g., Microsoft ActiveX Control), widgets (e.g., Eclipse's Standard Widget Toolkit, Google Web Toolkit), which allow users to interact with (or control) the application.

Types of containers

1.Window

The window is the container that have no borders and menu bars. You must use frame, dialog or another window for creating a window.

2.Panel

The Panel is the container that doesn't contain title bar and menu bars. It can have other components like button, textfield etc.

3.Frame

The Frame is the container that contain title bar and can have menu bars. It can have other components like button, textfield etc.

4.Dialog

 Dialog class has border and title. An instance of the Dialog class cannot exist without an associated instance of the Frame class.

AWT Container Classes

Ø  Top-Level Containers: Frame, Dialog and Applet

Ø  Secondary Containers: Panel and ScrollPane

AWT Component Classes

AWT provides many ready-made and reusable GUI components in package java.awt. The frequently-used are: Button, TextField, Label, Checkbox, CheckboxGroup (radio buttons), List, and Choice, as illustrated below.

AWT Components

A component is an object with a graphical representation that can be displayed on the screen and that can interact with the user. The Component class is the abstract parent of the nonmenu-related AWT components.Following is the list of commonly used controls while designed GUI using AWT.

Control & Description

Label A Label object is a component for placing text in a container.

Button This class creates a labeled button.

Checkbox A check box is a graphical component that can be in either an on (true) or off (false) state.

Radio Button OR Check Box Groups The CheckboxGroup class is used to group the set of checkbox.

List The List component presents the user with a scrolling list of text items.

Text Field A TextField object is a text component that allows for the editing of a single line of text.

Text Area A TextArea object is a text component that allows for the editing of a multiple lines of text.

Canvas A Canvas control represents a rectangular area where application can draw something or can receive inputs created by user.

Image An Image control is superclass for all image classes representing graphical images.