Answer: Short Notes on Web & Java Technologies

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(a) HTML Commands (Tags & Elements)

HTML (HyperText Markup Language) commands (commonly referred to as HTML tags and elements) are syntax keywords enclosed within angle brackets (<tagname>) used to define the structure, content, and hypermedia links of a webpage.

Core HTML Command Categories:

1. Document Skeleton Commands:
   • <!DOCTYPE html>: Declares HTML5 document type.
   • <html>, <head>, <body>: Defines the root, metadata, and visible document body.
2. Text Formatting Commands:
   • <h1> to <h6>: Headings; <p>: Paragraph; <br>: Line break; <hr>: Horizontal rule.
3. Hyperlinks & Media Commands:
   • <a href="...">: Creates clickable hyperlinks.
   • <img src="..." alt="...">: Embeds images.
4. Lists & Tables:
   • <ul>, <ol>, <li>: Unordered (bulleted) and ordered (numbered) lists.
   • <table>, <tr>, <th>, <td>: Renders structured tabular data.
5. Interactive Forms:
   • <form>, <input>, <select>, <button>, <textarea>: Collects user data.

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(b) DHTML Dragging and Dropping

DHTML (Dynamic HTML) is not a standalone language, but rather the synergistic combination of HTML, CSS, JavaScript, and the Document Object Model (DOM) to create interactive, animated web pages.

Drag and Drop Mechanism:

Drag and Drop allows users to click, grab an onscreen element, drag it over a target zone, and drop it.

[Draggable Element] -- (dragstart) --> [Dragging Over Target] -- (drop) --> [Dropped Element]
 (draggable="true")                     (event.preventDefault())             (dataTransfer)

Core HTML5 / DHTML Drag-and-Drop Events:

• dragstart: Fires when the user starts dragging an element. Uses event.dataTransfer.setData("text", target.id) to store data.
• dragover: Fires continuously when a dragged element is over a valid drop target. Must invoke event.preventDefault() to allow dropping.
• drop: Fires when the dragged item is released over the drop target. Retrieves data via event.dataTransfer.getData("text").

<div id="dragItem" draggable="true" ondragstart="event.dataTransfer.setData('text', this.id)">
  Drag Me
</div>
<div id="dropZone" ondragover="event.preventDefault()" ondrop="this.appendChild(document.getElementById(event.dataTransfer.getData('text')))">
  Drop Zone
</div>

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(c) AWT (Abstract Window Toolkit)

AWT (java.awt) is Java's original, platform-dependent Graphical User Interface (GUI) framework introduced in JDK 1.0.

                               +-----------------------------+
                               |          Component          |
                               +--------------+--------------+
                                              |
                     +------------------------+------------------------+
                     |                                                 |
                     v                                                 v
           +--------------------+                            +--------------------+
           |  Basic Controls    |                            |     Container      |
           | Button, Checkbox,  |                            | (Panel, Window,    |
           | Label, TextField   |                            |  Frame, Dialog)    |
           +--------------------+                            +--------------------+

Key Features of AWT:

1. Heavyweight Components: AWT components rely directly on the underlying operating system's native GUI peer widgets (e.g., a java.awt.Button creates a native Windows button on Windows and a Motif button on Unix).
2. Container Hierarchy:
   • Frame: Top-level window with a title bar, border, and minimize/maximize buttons.
   • Panel: Space-allocating container used to group components.
3. Layout Managers: Automatically arrange component geometry (FlowLayout, BorderLayout, GridLayout, GridBagLayout).
4. Event Delegation Model: Decouples event sources (e.g., Button) from event listeners (ActionListener, MouseListener).

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(d) JDBC (Java Database Connectivity)

JDBC (java.sql / javax.sql) is the standard Java API specification that enables Java applications to interact independently with relational database management systems (RDBMS like MySQL, Oracle, PostgreSQL).

+-----------------------+
|   Java Application    |
+-----------+-----------+
            | (JDBC API Calls)
            v
+-----------------------+
|  JDBC DriverManager   |
+-----------+-----------+
            |
            v
+-----------------------+
|   JDBC Driver (MySQL) |
+-----------+-----------+
            | (Database Protocol)
            v
+-----------------------+
|   RDBMS Database      |
+-----------------------+

Standard 5 Steps to Execute JDBC Operations:

1. Load Driver Class:

   Class.forName("com.mysql.cj.jdbc.Driver");
   

2. Establish Database Connection:

   Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/db", "root", "password");
   

3. Create Statement:

   Statement stmt = con.createStatement();
   // Or PreparedStatement for parameterized SQL
   

4. Execute SQL Query:

   ResultSet rs = stmt.executeQuery("SELECT * FROM students");
   while (rs.next()) {
       System.out.println(rs.getInt("roll_no") + " : " + rs.getString("name"));
   }
   

5. Close Resources:

   rs.close(); stmt.close(); con.close();