Online Java Compiler

Welcome to the world of Java! For decades, Java has been a dominant force in the programming world, famous for its "write once, run anywhere" philosophy. It's the backbone of massive enterprise applications, Android mobile apps, and large-scale web systems.

Java is an object-oriented language, meaning it structures code around "objects" and "classes," which helps in building large, organized, and maintainable software. This online compiler allows you to compile and run your Java code instantly, with no JDK installation required.

Write Java Code: Type your Java code in the editor. Make sure your main class is named Main.

Click Run: We'll compile your .java file into bytecode and then execute it using the Java Virtual Machine (JVM).

See Your Output: The program's output will be displayed in the result console.

Your First Java Program: "Hello, World!"

A Java "Hello, World!" program introduces you to the basic structure of a class.

  public class Main {
    public static void main(String[] args) {
        System.out.println("Hello, Java explorers at docodehere.com!");
    }
}

public class Main { ... }: In Java, all code lives inside a class. This is the main container for your program. Our compiler requires this class to be named Main.

public static void main(String[] args) { ... }: This is the main method. It's the specific entry point where the Java Virtual Machine (JVM) starts running your program.

System.out.println(...): This is the command to print a line of text to the console. It's Java's version of print or console.log.

Let's Try Something More: A Simple Loop

Loops are fundamental for repeating tasks. Let's write a for loop that counts from 1 to 5.

  public class Main {
    public static void main(String[] args) {
        System.out.println("Let's start counting...");

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

        System.out.println("...Counting finished!");
    }
}

This code initializes a variable i at 1, runs the loop as long as i is less than or equal to 5, and increases i by one after each cycle (i++).

The Java Virtual Machine (JVM) is the magic that makes Java platform-independent. You compile your code once into a universal "bytecode," and the JVM on any machine (Windows, Mac, Linux) knows how to run that bytecode.

Java is strictly Object-Oriented. A class is a blueprint for creating objects, which bundle data and the methods that operate on that data. Even a simple program needs to be inside a class structure.

This is a very common runtime error in Java. It means you tried to use an object variable that doesn't point to an actual object yet (its value is null). You need to create an instance of the object before you can use it.

Start your Java journey here. Happy coding!