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1. Hello World:
public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"); } }
2. Variables and Data Types:
// Variable declaration int num1 = 10; double num2 = 3.14; String name = "John"; // Primitive data types int, double, char, boolean // Reference data types String, Arrays, Classes, etc.
3. Control Flow:
// If-else statement if (condition) { // code block } else if (anotherCondition) { // code block } else { // code block } // Switch statement int day = 2; switch (day) { case 1: // code block break; case 2: // code block break; default: // code block } // While loop while (condition) { // code block } // For loop for (int i = 0; i < 5; i++) { // code block } // For-each loop (enhanced for loop) int[] numbers = {1, 2, 3, 4, 5}; for (int number : numbers) { // code block }
4. Functions (Methods):
// Method declaration public returnType methodName(parameters) { // code block return returnValue; // returnType should match the declared type } // Example public int add(int a, int b) { return a + b; }
5. Object-Oriented Programming (OOP): // Class declaration class MyClass { // Fields (variables) int field1; String field2; // Constructor public MyClass(int value, String name) {
field1 = value; field2 = name; } // Methods public void method1() { // code block } } // Object creation MyClass obj = new MyClass(42, "John"); // Accessing fields and methods int value = obj.field1; String name = obj.field2; obj.method1();
6. Arrays:
// Array declaration int[] numbers = new int[5]; // creates an array of size 5 int[] numbers = {1, 2, 3, 4, 5}; // initializes array with values // Accessing array elements int firstElement = numbers[0]; // Array length int length = numbers.length;
## 7. Input/Output: import java.util.Scanner; **_// Import Scanner class for user input // Reading user input_** Scanner scanner = new Scanner(System.in); int num = scanner.nextInt(); String input = scanner.nextLine(); ## 8. Exception Handling: try { _// code that might cause an exception_ } catch (ExceptionType1 ex1) { _// exception handling for ExceptionType_ } catch (ExceptionType2 ex2) { _// exception handling for ExceptionType_ } finally { _// optional code block that runs regardless of exceptions_ } ## 9. Inheritance: **_// Parent class_** class Animal { void sound() { System.out.println("Animal makes a sound."); } } **_// Child class_** class Dog extends Animal { void sound() { System.out.println("Dog barks."); } } ## 10. Interfaces: _// Interface declaration_ interface MyInterface { void doSomething(); } _// Implementing the interface_ class MyClass implements MyInterface { public void doSomething() { // code block } }
