java chapter 1

1. What is Java?

• Java is a high-level, object-oriented, and platform-independent programming language developed by James Gosling at Sun Microsystems in 1995.
• Initially called Oak, later renamed Java.
• Java programs are compiled into bytecode, which can run on any machine that has a Java Virtual Machine (JVM).

2. Features of Java

1. Simple – Easy to learn and use.
2. Object-Oriented – Everything is treated as an object.
3. Platform-Independent – “Write Once, Run Anywhere” (WORA).
4. Secure – No explicit pointers, runs inside JVM sandbox.
5. Robust – Strong memory management and exception handling.
6. Multithreaded – Supports multiple threads (parallel execution).
7. Portable – Bytecode works across platforms.
8. High Performance – Uses Just-In-Time (JIT) compiler.
9. Distributed – Can be used for internet-based applications.

3. Java Editions

• JSE (Java Standard Edition): Core Java for desktop applications.
• JEE (Java Enterprise Edition): For web and enterprise applications.
• JME (Java Micro Edition): For mobile and embedded devices.

4. Java Program Structure

Example:

class Hello {
    public static void main(String args[]) {
        System.out.println("Hello, World!");
    }
}

Explanation:

• class → defines a class.
• main() → entry point of Java program.
• System.out.println() → displays output.

5. Java Compilation Process

1. Write code → Hello.java
2. Compile → javac Hello.java (creates Hello.class)
3. Run → java Hello
4. JVM executes bytecode.

6. Java Virtual Machine (JVM)

• Converts bytecode into machine code.
• Provides platform independence.
• Handles memory management and garbage collection.

7. Tokens in Java

Basic building blocks:

• Keywords (e.g., class, public, static, if, else)
• Identifiers (names of variables, classes, methods)
• Literals (constants like 10, "Hello")
• Operators (+, -, *, /, %, ==, etc.)
• Separators (;, {}, [], ())
• Comments (// for single-line, /* */ for multi-line)

8. Data Types in Java

• Primitive: byte, short, int, long, float, double, char, boolean.
• Non-Primitive: String, Arrays, Classes, Interfaces.

9. Variables and Constants

• Variable: stores data value.int age = 18;
• Constant: defined using final keyword.final double PI = 3.14;

10. Operators

• Arithmetic, Relational, Logical, Assignment, Unary, Ternary, etc.

11. Input and Output in Java

import java.util.Scanner;
Scanner sc = new Scanner(System.in);
int num = sc.nextInt();
System.out.println("Number = " + num);

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🧾 In Short

• Java = Simple + Object-Oriented + Platform Independent.
• Code → Bytecode → JVM → Execution.
• Java programs run safely and consistently across platforms.