java

Java Language Tutorial

1. What is Java?

Java is a high-level, class-based, object-oriented programming language. It is widely used for building platform-independent applications, ranging from mobile apps to enterprise systems.

2. How to Install Java?

1. Download the Java Development Kit (JDK) from the official Oracle website or OpenJDK.
2. Install the JDK by following the setup instructions.
3. Set the JAVA_HOME environment variable and update the PATH variable.
4. Verify the installation by running java -version in the terminal.

3. Your First Java Program

Let’s write our first Java program:

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

Save this code in a file named HelloWorld.java, then compile and run it:

• To compile: javac HelloWorld.java
• To run: java HelloWorld

4. Variables and Data Types

In Java, variables are declared with specific data types. Here are some common data types:

public class DataTypes {
    public static void main(String[] args) {
        int x = 10;       // Integer
        float y = 3.14f;  // Float
        char letter = 'A'; // Character
        String name = "Java"; // String

        System.out.println("x = " + x + ", y = " + y + ", letter = " + letter + ", name = " + name);
    }
}

5. Conditional Statements

Conditional statements in Java include if, else if, and else.

public class ConditionalStatements {
    public static void main(String[] args) {
        int num = 10;
        if (num > 0) {
            System.out.println("Positive number");
        } else if (num == 0) {
            System.out.println("Zero");
        } else {
            System.out.println("Negative number");
        }
    }
}

6. Loops

Java supports for, while, and do-while loops.

For Loop:

public class ForLoop {
    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            System.out.println(i);
        }
    }
}

While Loop:

public class WhileLoop {
    public static void main(String[] args) {
        int count = 0;
        while (count < 5) {
            System.out.println(count);
            count++;
        }
    }
}

7. Methods

Methods in Java help to modularize code.

public class Methods {
    public static void greet(String name) {
        System.out.println("Hello, " + name + "!");
    }

    public static void main(String[] args) {
        greet("Alice");
    }
}

8. Arrays

Arrays in Java are used to store multiple values of the same data type.

public class Arrays {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};
        for (int num : numbers) {
            System.out.println(num);
        }
    }
}

9. Classes and Objects

Classes and objects are fundamental to Java's object-oriented programming.

public class Student {
    String name;
    int age;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public void displayInfo() {
        System.out.println("Name: " + name + ", Age: " + age);
    }

    public static void main(String[] args) {
        Student s1 = new Student("John", 21);
        s1.displayInfo();
    }
}

10. File Handling

File handling in Java is done using classes from the java.io package.

import java.io.*;

public class FileHandling {
    public static void main(String[] args) {
        try {
            FileWriter writer = new FileWriter("example.txt");
            writer.write("Hello, Java!");
            writer.close();

            BufferedReader reader = new BufferedReader(new FileReader("example.txt"));
            String line = reader.readLine();
            System.out.println(line);
            reader.close();
        } catch (IOException e) {
            System.out.println("An error occurred: " + e.getMessage());
        }
    }
}

11. Inheritance

Inheritance in Java allows one class to inherit the fields and methods of another class.

class Animal {
    void sound() {
        System.out.println("Animal makes a sound");
    }
}

class Dog extends Animal {
    void sound() {
        System.out.println("Dog barks");
    }
}

public class Inheritance {
    public static void main(String[] args) {
        Animal a = new Dog();
        a.sound();
    }
}

12. Java Libraries

Java has a rich set of libraries for various functionalities. Some commonly used libraries are:

• java.util: For data structures like ArrayList and HashMap.
• java.io: For input/output operations.
• java.net: For network operations.
• java.time: For date and time manipulation.