Java AWT, Applets, 4GL, and Oracle Database Essentials
AWT, Applets, and Applications
The Abstract Window Toolkit (AWT) provides fundamental components for creating Graphical User Interfaces (GUIs) used in both Java applications and applets. A key advantage of AWT is its platform independence, ensuring consistent display across different operating systems and graphical interfaces.
AWT study strategy can be divided into:
- Components: Classes and interfaces for creating GUI objects like buttons, dropdown lists, text boxes, checkboxes, radio buttons, labels, and menus.
- Containers: Classes and interfaces for grouping components, such as panels, dialog boxes, frames, and windows.
- Layouts (Design Managers): Classes and interfaces for managing the arrangement and positioning of components within containers (e.g., FlowLayout, BorderLayout).
- Events: Classes and interfaces for handling user interactions and other actions within the GUI.
Components:
Button: A component to receive mouse clicks.
Label: A component displaying a text string.
List: A component containing a dynamic set of elements.
Containers:
Containers hold components, added using the add() method. Key container types include Panel and Window.
Layouts:
Layout managers control component placement. For instance, FlowLayout arranges components sequentially, while BorderLayout divides the container into five regions (north, south, east, west, center). Layouts are set using the setLayout() method and determine component sizing.
Events:
Events represent user actions (e.g., button clicks, key presses) or system actions (e.g., timers). Event handling makes GUIs interactive and responsive.
Using AWT with Applets
AWT provides the building blocks for GUIs in both applications and applets. Applets can utilize almost all AWT classes (Frame, Dialog, Window, Container, etc.), except for the Menu class. An example demonstrating AWT in applets for graphing functions will be presented later.
Life Cycle of a Thread
4GL: Fourth Generation Languages
Fourth-generation languages (4GLs) offer a high level of abstraction, allowing programmers to focus on *what* the application should do rather than *how* to do it. This results in significantly less code compared to third-generation languages (3GLs). 4GLs are characterized by powerful tools and a closer resemblance to human language, enhancing clarity and understandability.
While 4GLs excel at automatic code generation and GUI prototyping, their capabilities in data management and functional processes have been somewhat limited. Early 4GLs heavily relied on GUI prototyping for code generation. The evolution of 4GLs has been influenced by operating system and hardware constraints, database integration, user interface demands, object-oriented programming, client/server architecture, and collaborative software engineering.
Object-oriented programming has led to the development of object libraries that enhance 4GL functionality, including access to relational and hierarchical databases, electronic messaging systems, workgroup systems, and advanced GUIs. However, further improvements are needed in process modeling and identifying the most crucial user processes. Different types of 4GLs and specific product examples will be discussed later.
What is Oracle?
Oracle Database, designed for Grid Computing, is a relational database management system produced by Oracle Corporation. It is a powerful and often expensive client/server database solution typically used by large multinational companies.
Oracle Features
Oracle Content Database, built on Oracle Database, manages large volumes of unstructured content in a single repository, reducing costs and information loss risks.
Oracle Structures
An Oracle database has both a physical and a logical structure:
- The physical structure corresponds to operating system files.
- The logical structure consists of tablespaces and objects within a database schema.