Java Programming Language Tutorial
Overview
Java is a high-level, object-oriented programming language known for its portability across platforms, robustness, and ease of use. It is widely used for building enterprise-scale applications, Android apps, and web applications.
Basic Syntax
Hello World
A simple program to print "Hello, World!" to the console.
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}
Comments
- Single-line comment:
// This is a single-line comment - Multi-line comment:
Data Types
Primitive Data Types
- int: Integer type
- float: Floating-point type
- double: Double precision floating-point type
- char: Character type
- boolean: Boolean type
Example
public class DataTypes {
public static void main(String[] args) {
int age = 25;
float height = 5.9f;
double weight = 70.5;
char initial = 'A';
boolean isStudent = true;
System.out.println("Age: " + age);
System.out.println("Height: " + height);
System.out.println("Weight: " + weight);
System.out.println("Initial: " + initial);
System.out.println("Is Student: " + isStudent);
}
}
Control Flow
If-Else Statement
public class IfElseExample {
public static void main(String[] args) {
int number = 10;
if (number > 0) {
System.out.println("The number is positive.");
} else if (number < 0) {
System.out.println("The number is negative.");
} else {
System.out.println("The number is zero.");
}
}
}
Switch Statement
public class SwitchExample {
public static void main(String[] args) {
int day = 3;
switch (day) {
case 1:
System.out.println("Monday");
break;
case 2:
System.out.println("Tuesday");
break;
case 3:
System.out.println("Wednesday");
break;
default:
System.out.println("Invalid day");
}
}
}
Methods
Method Declaration and Definition
public class MethodsExample {
public static void greet() {
System.out.println("Hello, welcome to Java programming!");
}
public static void main(String[] args) {
greet();
}
}
Method with Parameters
public class AddExample {
public static int add(int a, int b) {
return a + b;
}
public static void main(String[] args) {
int sum = add(5, 7);
System.out.println("Sum: " + sum);
}
}
Classes and Objects
Defining a Class
public class Person {
String name;
int age;
void introduce() {
System.out.println("Hi, my name is " + name + " and I am " + age + " years old.");
}
public static void main(String[] args) {
Person person1 = new Person();
person1.name = "Alice";
person1.age = 30;
person1.introduce();
}
}
Inheritance and Polymorphism
Inheritance Example
public class Animal {
public void speak() {
System.out.println("Animal makes a sound.");
}
}
public class Dog extends Animal {
@Override
public void speak() {
System.out.println("Dog barks.");
}
public static void main(String[] args) {
Dog myDog = new Dog();
myDog.speak(); // Calls the Dog's speak method
}
}
Polymorphism Example
public class Base {
public void show() {
System.out.println("Base class");
}
}
public class Derived extends Base {
@Override
public void show() {
System.out.println("Derived class");
}
public static void main(String[] args) {
Base obj = new Derived();
obj.show(); // Calls Derived's show method
}
}
Interfaces and Abstract Classes
Interface Example
interface Drawable {
void draw();
}
public class Circle implements Drawable {
@Override
public void draw() {
System.out.println("Drawing a circle.");
}
public static void main(String[] args) {
Circle circle = new Circle();
circle.draw();
}
}
Abstract Class Example
abstract class Animal {
abstract void makeSound();
void sleep() {
System.out.println("This animal sleeps.");
}
}
public class Cat extends Animal {
@Override
void makeSound() {
System.out.println("Meow");
}
public static void main(String[] args) {
Cat cat = new Cat();
cat.makeSound();
cat.sleep();
}
}
Exception Handling
Try-Catch Block
public class ExceptionHandlingExample {
public static void main(String[] args) {
try {
int[] numbers = {1, 2, 3};
System.out.println(numbers[5]); // This will throw an ArrayIndexOutOfBoundsException
} catch (ArrayIndexOutOfBoundsException e) {
System.out.println("Exception caught: " + e.getMessage());
} finally {
System.out.println("This block is always executed.");
}
}
}
File I/O
Reading from a File
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class FileReadExample {
public static void main(String[] args) {
try (BufferedReader br = new BufferedReader(new FileReader("example.txt"))) {
String line;
while ((line = br.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
System.out.println("An error occurred: " + e.getMessage());
}
}
}
Writing to a File
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
public class FileWriteExample {
public static void main(String[] args) {
try (BufferedWriter bw = new BufferedWriter(new FileWriter("output.txt"))) {
bw.write("This is a test file.");
} catch (IOException e) {
System.out.println("An error occurred: " + e.getMessage());
}
}
}
Java Collections Framework
Using ArrayList
import java.util.ArrayList;
public class ArrayListExample {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<>();
list.add("Apple");
list.add("Banana");
list.add("Cherry");
for (String fruit : list) {
System.out.println(fruit);
}
}
}
Using HashMap
import java.util.HashMap;
public class HashMapExample {
public static void main(String[] args) {
HashMap<String, Integer> map = new HashMap<>();
map.put("Alice", 30);
map.put("Bob", 25);
for (String key : map.keySet()) {
System.out.println(key + " is " + map.get(key) + " years old.");
}
}
}
Summary
This tutorial covers the basic concepts and syntax of Java programming. Java is a versatile language that supports object-oriented principles and provides a rich set of libraries for various applications. For further learning, refer to the Java Tutorials by Oracle.