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Online Java Compiler and Playground

Browser-based compiler and playground for Java — Progsity IDE.

About Java

Java powers Android apps, enterprise backends, and large open-source ecosystems. This online Java compiler runs a standard public static void main entry point so you can practice OOP, collections, and exceptions in a browser—no JDK install required on your laptop.

The sandbox compiles and executes your class in isolation. You will see compilation errors separately from runtime stack traces, which mirrors how IDEs present feedback in real projects.

Great for university assignments, certification prep, and quick experiments with Scanner-based stdin. Sign in to save snippets and share links with classmates.

How to use

  1. Keep your code inside class Main with a public static void main(String[] args) method unless you change the template.
  2. Use Scanner or BufferedReader on System.in for stdin; paste matching input in the stdin panel.
  3. If compilation fails, fix package/import issues first, then re-run.

FAQ

Is this Java compiler free?›

Yes. Running Java programs is free. Snippet storage may be limited for free accounts.

Which Java version?›

The runtime matches a modern LTS-style JDK in the Judge0 environment. For version checks, print System.getProperty("java.version").

Can I use multiple classes?›

Single-file playgrounds expect one public top-level class named Main. For larger designs, split logic mentally or use static nested classes in one file.

Can I save code?›

Yes when signed in. Access from Dashboard → Playground.

Compiler vs playground?›

You get a compiler (javac-style step) plus instant run—classic playground flow for learning Java.

Related languages

Code examples

Tap “Try this” to load sample code into the editor above.

  • Scanner sum

    import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        System.out.println(a + b);
    }
}

  • For loop

    public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            System.out.println(i);
        }
    }
}

  • ArrayList

    import java.util.*;

public class Main {
    public static void main(String[] args) {
        List<String> xs = new ArrayList<>();
        xs.add("a");
        xs.add("b");
        System.out.println(xs.size());
    }
}

  • String reverse

    public class Main {
    public static void main(String[] args) {
        String s = "drawer";
        System.out.println(new StringBuilder(s).reverse());
    }
}