Learn Java

Java Topics

Click on a topic to expand and learn in detail.

• 1. Introduction to Java

Java is a high-level, object-oriented programming language used for desktop, web, and mobile applications.

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

• 2. Variables & Data Types

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

• 3. Operators

// Arithmetic: +, -, *, /, %
int sum = 5 + 3;

// Comparison: ==, !=, >, <
boolean result = (5 > 3);

// Logical: &&, ||, !
boolean flag = true && false;
      

• 4. Conditions (if, else, switch)

int age = 18;

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

switch(age){
    case 18:
        System.out.println("Exactly 18");
        break;
    default:
        System.out.println("Other age");
}
      

• 5. Loops (for, while, do-while)

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

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

// do-while loop
int j=0;
do{
    System.out.println(j);
    j++;
}while(j<5);
      

• 6. Methods / Functions

public static int add(int a, int b){
    return a + b;
}

public static void main(String[] args){
    System.out.println(add(5,3));
}
      

• 7. Arrays & Strings

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

String name = "Alice";
System.out.println(name);
      

• 8. Object-Oriented Programming (OOP)

class Person {
    String name;
    int age;

    void greet(){
        System.out.println("Hello " + name);
    }
}

public class Main {
    public static void main(String[] args){
        Person p = new Person();
        p.name = "Alice";
        p.age = 25;
        p.greet();
    }
}
      

• 9. Exception Handling

try{
    int result = 10 / 0;
}catch(ArithmeticException e){
    System.out.println("Cannot divide by zero");
}finally{
    System.out.println("Execution finished");
}
      

• 10. Collections Framework
• ArrayList, LinkedList
• HashMap, HashSet
• Iterators & Loops
• Sorting & Searching
• 11. Advanced Java Topics
• Java Generics
• Java Streams
• Lambda Expressions
• Multithreading
• File I/O
• Serialization & Deserialization
• JavaFX / Swing Basics
• Networking in Java
• Java Modules