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Basics of Java Programming

• Java is a high-level, object-oriented, platform-independent programming language.
• Java code is written inside classes and the program execution starts from the main method:

    
    public class MyClass {
        public static void main(String[] args) {
            // Code goes here
        }
    }
    
    

Key Concepts:
• Class → Blueprint for objects
• Method → Block of code that performs a task
• Main Method → public static void main(String[] args) (starting point of program)

Hello World Program

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

Explanation:

• System.out.println() 

  → prints a line on the console.
• The file should be saved as

  HelloWorld.java

  (same as class name).

Variables and Data Types

Variables
• Variable → A name that refers to a value stored in memory.
• Declared with a data type.

Example:

    
    int age = 25;
    double pi = 3.14;
    char grade = 'A';
    boolean isJavaFun = true;
    String name = "Alice";
    
    

Data Types

Type	Description	Example
int	Integer numbers	int x = 10;
double	Decimal numbers	double pi = 3.14;
char	Single character	char c = 'A';
boolean	True or false	boolean flag = true;
String	Text (sequence of characters)	String str = "Java";

Operators in Java

Arithmetic Operators

Operator	Meaning	Example
+	Addition	a + b
-	Subtraction	a - b
*	Multiplication	a * b
/	Division	a / b
%	Modulus (remainder)	a % b

Example:

    
    int a = 10, b = 3;
    System.out.println(a + b); // 13
    System.out.println(a % b); // 1
    
    

Relational Operators

Operator	Meaning	Example
+	Addition	a + b
-	Subtraction	a - b
*	Multiplication	a * b
/	Division	a / b
%	Modulus (remainder)	a % b
==	Equal to	a == b
!=	Not equal to	a != b
>	Greater than	a > b
<	Less than	a < b
>=	Greater than or equal to	a >= b
<=	Less than or equal to	a <= b

Example:

    
        System.out.println(5 > 3); // true
    
    

Logical Operators

Operator	Meaning	Example
&&	Logical AND	(a > 0 && b > 0)
`		`
!	Logical NOT	!(a > b)

Example:

    
    System.out.println((5 > 3) && (8 > 5)); // true
    System.out.println(!(5 == 5)); // false
    
    

Input and Output

Output (Display something)

Use

System.out.print()

and

System.out.println()

    
    System.out.println("Hello Java");  // prints with a new line
    System.out.print("Hello ");        // prints without new line
    System.out.print("Java");
    
    

Input (Take user input)

Use Scanner class from java.util package.

Example:

    
    import java.util.Scanner;

    public class InputExample {
        public static void main(String[] args) {
            Scanner input = new Scanner(System.in); // create scanner object

            System.out.print("Enter your name: ");
            String name = input.nextLine();          // read a full line

            System.out.print("Enter your age: ");
            int age = input.nextInt();                // read an integer

            System.out.println("Hello, " + name + ". You are " + age + " years old.");
        }
    }
    
    

Important Scanner methods:

• nextLine() → read a line of text
• nextInt() → read an integer
• nextDouble() → read a decimal number
• next() → read a single word (without spaces)

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