Learn Java: The Complete Beginner’s Guide

Java is one of the world’s most widely used programming languages. It is object-oriented, platform-independent, and the backbone of many enterprise applications, Android apps, and server systems.

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Why Learn Java?

• Cross-platform → Runs on any OS with a JVM (Write Once, Run Anywhere).
• Object-Oriented → Organize code into reusable classes.
• Popular → Used in Android, backend, finance, and more.
• Stable & Secure → Trusted for enterprise-level software.

Hello World

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

Variables

int age = 25;            // Integer
double pi = 3.14;        // Decimal
String name = "Alice";   // Text
boolean isJavaFun = true; // Boolean

Data Types

• Primitive Types: int, double, char, boolean
• Non-Primitive Types: String, Arrays, Objects

Operators

• + (addition), - (subtraction)
• * (multiplication), / (division)
• == (equal to), != (not equal)
• && (AND), || (OR)

Conditionals

int age = 18;

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

Switch Statement

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("Other day");
}

Loops

for (int i = 1; i <= 5; i++) {
    System.out.println(i);
}

int x = 0;
while (x < 3) {
    System.out.println(x);
    x++;
}

Methods

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

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

Classes and Objects

class Person {
    String name;
    int age;

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

    void greet() {
        System.out.println("Hi, I'm " + name + " and I'm " + age + " years old.");
    }
}

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

Inheritance

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

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

public class Main {
    public static void main(String[] args) {
        Dog d = new Dog();
        d.sound();
    }
}

Arrays

int[] numbers = {1, 2, 3, 4};
for (int n : numbers) {
    System.out.println(n);
}

Mini Project: Simple Calculator

import java.util.Scanner;

public class Calculator {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter first number: ");
        int a = sc.nextInt();
        System.out.print("Enter second number: ");
        int b = sc.nextInt();

        System.out.println("Sum: " + (a + b));
        System.out.println("Difference: " + (a - b));
    }
}

Best Practices

• Follow naming conventions (camelCase for variables, PascalCase for classes).
• Keep classes small and focused.
• Use comments to explain complex logic.
• Avoid unnecessary object creation.

Next Steps

1. Java Collections → Learn about lists, sets, and maps.
2. OOP Principles → Deep dive into inheritance, polymorphism, encapsulation.
3. Frameworks → Spring Boot for backend development.
4. Android → Learn Java for mobile apps (though Kotlin is now preferred).

Conclusion

Java is a powerful, stable, and versatile programming language that has shaped modern software development. Mastering Java will give you a solid foundation for Android apps, enterprise applications, and backend systems.

Keep practicing, build projects, and Java will open countless opportunities 🚀🔥