Java Programming Basics

 ✅ 1. Your First Java Program

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

• public class HelloWorld: Java code must be inside a class.

• main(String[] args): Entry point of any Java program.

• System.out.println(): Prints output to the console.

✅ 2. Variables and Data Types

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int age = 25; double price = 19.99; char grade = 'A'; boolean isJavaFun = true; String name = "Alice";

Type	Description	Example
int	Integer	5
double	Decimal number	3.14
char	Single character	'A'
boolean	True or false	true / false
String	Text (object)	" Hello"

✅ 3. Operators

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int x = 10 + 5; // 15 int y = 10 * 2; // 20 int z = x / 3; // 5

• +, -, *, /, %: Arithmetic

• ==, !=, >, <, >=, <=: Comparison

• &&, ||, !: Logical

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✅ 4. Control Statements

if Statement

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if (age > 18) { System.out.println("Adult"); } else { System.out.println("Minor"); }

switch Statement

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int day = 3; switch (day) { case 1: System.out.println("Monday"); break; case 2: System.out.println("Tuesday"); break; default: System.out.println("Other day"); }

✅ 5. Loops

for Loop

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for (int i = 0; i < 5; i++) { System.out.println(i); }




while Loop

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int i = 0; while (i < 5) { System.out.println(i); i++; }

✅ 6. Arrays

1 2	int[] numbers = {1, 2, 3, 4, 5}; System.out.println(numbers[0]); // 1

✅ 7. Methods (Functions)

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public static int add(int a, int b) { return a + b; } // Usage: int result = add(3, 4); // 7

✅ 8. Classes and Objects

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public class Car { String color; public void drive() { System.out.println("Car is driving"); } } // In another class or in main() Car myCar = new Car(); myCar.color = "Red"; myCar.drive();

✅ 9. Comments

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// This is a single-line comment /* This is a multi-line comment */

✅ 10. Compile and Run Java

Assuming your file is HelloWorld.java:

javac HelloWorld.java   # Compiles the code

java HelloWorld         # Runs the program