Online Java Compiler

Compile and run Java classes online using a CLI-style tool—no JDK installation required.

Version

Sample

🚀 43,745 total executions (5,083 this month)

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☕ About This Java Online Executor

The CodeUtility Java Executor lets you write and run Java programs directly in your browser — no installation, JDK setup, or IDE required. It’s powered by a secure sandbox that supports real Java runtime versions 8, 11, 17, 21, and the latest.

This tool compiles and executes Java code in the cloud using a real javac compiler and Java runtime environment, so you can test classes, methods, and logic exactly as they would behave locally.

Whether you’re practicing object-oriented programming, preparing for interviews, or testing snippets before integration, the CodeUtility Java Executor provides a fast and reliable environment to run real Java code instantly from any device.

⚙️ How to Use This Tool

1. Select a Java version (8, 11, 17, 21, or Latest) from the dropdown at the top of the editor.
2. Write or paste your Java code into the editor area.
3. Click Run to compile and execute your program — output will appear in the console below.
4. While running, a Stop button appears — click it to stop execution early.
5. Use Fix Code to automatically correct minor formatting or syntax issues.
6. After fixing, a Fixes button appears — click it to review recent fixes.
7. Use the Upload button to import code from a local file, or the Download button to save your current code from the editor.
8. Each execution runs up to 20 seconds before automatically terminating.

🧠 Tip: This environment runs real Java code securely in your browser — no login or setup required.

💡 Java Basics & Examples You Can Try Above

1. Declaring Variables and Constants

Java requires you to declare the type of each variable. Use final for constants.

int age = 30;
double pi = 3.14159;
char grade = 'A';
String name = "Alice";
boolean isActive = true;

// Constants
final int MAX_USERS = 100;
final String COMPANY = "CodeUtility";

2. Conditionals (if / switch)

Use if, else if, and switch for control flow.

int x = 2;
if (x == 1) {
    System.out.println("One");
} else if (x == 2) {
    System.out.println("Two");
} else {
    System.out.println("Other");
}

switch (x) {
    case 1:
        System.out.println("One");
        break;
    case 2:
        System.out.println("Two");
        break;
    default:
        System.out.println("Other");
}

3. Loops

Use for, while, and do-while for iteration.

for (int i = 0; i < 3; i++) {
    System.out.println(i);
}

int n = 3;
while (n > 0) {
    System.out.println(n);
    n--;
}

4. Arrays

Arrays hold fixed-size sequences of the same type.

int[] numbers = {10, 20, 30};
System.out.println(numbers[1]);

5. ArrayList Manipulation

Use ArrayList for dynamic-sized lists.

import java.util.ArrayList;

ArrayList<Integer> nums = new ArrayList<>();
nums.add(1);
nums.add(2);
nums.add(3);
nums.remove(Integer.valueOf(2));

for (int num : nums) {
    System.out.print(num + " ");
}

6. Console Input/Output

Use Scanner for input and System.out for output.

import java.util.Scanner;

Scanner scanner = new Scanner(System.in);
System.out.print("Enter your name: ");
String name = scanner.nextLine();
System.out.println("Hello, " + name);

7. Functions

Define methods with return types and parameters.

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

System.out.println(add(3, 4));

8. HashMaps

Use HashMap for key-value storage.

import java.util.HashMap;

HashMap<String, Integer> ages = new HashMap<>();
ages.put("Alice", 30);
System.out.println(ages.get("Alice"));

9. Exception Handling

Use try and catch to handle runtime exceptions.

try {
    throw new Exception("Something went wrong");
} catch (Exception e) {
    System.out.println(e.getMessage());
}

10. File I/O

Use Files and Paths from java.nio.file for file handling.

import java.nio.file.*;
import java.io.IOException;

Files.writeString(Paths.get("file.txt"), "Hello File");
String content = Files.readString(Paths.get("file.txt"));
System.out.println(content);

11. String Manipulation

Java strings support many methods like length(), substring(), and contains().

String text = "Hello World";
System.out.println(text.length());
System.out.println(text.substring(0, 5));
System.out.println(text.contains("World"));

12. Classes & Objects

Java supports object-oriented programming using classes and instances.

class Person {
    String name;
    Person(String name) {
        this.name = name;
    }
    void greet() {
        System.out.println("Hi, I'm " + name);
    }
}

Person p = new Person("Alice");
p.greet();