MSBTE Diploma: Java AWT Chapter 1

Abstract Windowing Toolkit (AWT)

• AWT is a Java API to develop graphical user interface (GUI) or windows-based applications.
• AWT components are platform-dependent, i.e., they are displayed according to the view of the operating system.
• AWT is heavy weight, i.e., its components use the resources of the underlying operating system (OS).
• AWT is a GUI library that provides packages and classes to add graphical components (e.g., buttons, text boxes, check boxes) to applications.

Features of AWT

• AWT is a set of native user interface components.
• It is based on a robust event-handling model.
• It provides graphics and imaging tools, such as shape, color, and font classes.
• AWT avails layout managers, which help in increasing the flexibility of window layouts.
• It includes data transfer classes that help in cut-and-paste through the native platform clipboard.

Container in Java

• A container is a component that holds other components.
• A container is a subclass of java.awt.Component and is responsible for keeping track of components being added.
• There are four types of containers:
  • Window: A window with neither border nor title.
  • Frame: A frame with title, border, and menu bars.
  • Dialog: A dialog with border and title.
  • Panel: A generic container for holding GUI components.

AWT Controls

• java.awt.Button: A labeled button that triggers a certain programmed action upon clicking.
• java.awt.TextField: A single-line text box for users to enter texts.
• java.awt.Label: A descriptive text string that is visible on the GUI.
• java.awt.Canvas: A rectangular area where you can draw or receive user inputs.
• java.awt.Choice: A pop-up menu of choices.
• java.awt.ScrollBar: A horizontal and vertical scrollbar in the GUI.
• java.awt.List: A list of text items.
• java.awt.CheckBox: A graphical component with two states: true and false.

Layout Managers

• Layout managers are used to arrange components in a particular manner.
• There are five types of layout managers:
  • java.awt.BorderLayout: Components are positioned in five different areas (regions): North, South, East, West, and Center.
  • java.awt.FlowLayout: Components are placed from left to right, as they were added.
  • java.awt.GridLayout: Components are placed in a grid of cells (rectangular).
  • java.awt.CardLayout: Manages two or more components that share the same display space, in such a way that only one component is visible at a time.
  • java.awt.GridBagLayout: A flexible layout manager that allows for complex layouts.

Example: Developing a Calculator with Java AWT

• A calculator application can be developed using AWT components, such as buttons, text fields, and labels.

• The application can perform basic mathematical operations, such as addition, subtraction, multiplication, and division.### Card Layout Manager

• Each card is like a playing card in a stack, where only the top card is visible at any time.

• The Card Layout Manager is used to manage components in a stack.

• Each card is normally a panel that can use any layout manager.

Flow Layout Manager

• Example code is provided to illustrate the use of FlowLayout.
• The FlowLayout is used to arrange components in a row or column.
• The FlowLayout class is used to create a flow layout manager.

GridBag Layout Manager

• The GridBag layout manager manages components in rows or columns, allowing specified components to span multiple rows and columns.
• Not all rows and columns have the same height and width.
• This is the most complex layout manager, as it specifies the size and position characteristics of its components by specifying constraints for each component.
• Example code is provided to illustrate the use of GridBagLayout.

Menu and Menu Bar

• The MenuItem class adds a simple labeled menu item on a menu.
• The Menu class is a pull-down menu component that is displayed on the menu bar.
• Menus are very familiar to programmers in the Windows environment.
• A menu has a pull-down list of menu items from which the user can select one at a time.
• A click on the MenuItem generates an ActionEvent and is handled by an ActionListener.
• A Menu and a MenuItem are not components, as they are not subclasses of the java.awt.Component class.
• They are derived from the MenuComponent class.

Menu Creation

• The procedure for creating menus involves:
  • Creating a menu bar
  • Adding the menu bar to the frame
  • Creating menus
  • Adding menus to the menu bar
  • Creating menu items
  • Adding menu items to menus
  • Event handling

Menu Hierarchy

• The MenuComponent is the highest level class of all menu classes.
• A MenuBar is capable of holding menus, and a Menu can hold menu items.
• Menus are placed on a menu bar.

MCQ Questions

• The abstract class that is the superclass of all menu-related classes is MenuComponent.
• The most commonly used layout managers are Flow layout, Border layout, and Grid layout.
• The default layout manager for subclasses of Window is BorderLayout.
• Each menu is associated with a drop-down list of menu items.