CodeUtility
Making your developer's life easier!

Lightweight Java IDE - Run Java Code Online

Write, run, and debug Java in a lightweight online IDE with multi-file editing, persistent workspaces, runtime libraries, sharing, and live collaboration.

Pre-installed Libs
🚀 214,090 total executions (2,223 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.

More than a code runner

Use a multi-file editor, an isolated execution terminal, runtime-specific libraries, persistent workspaces, sharing, and real-time collaboration from the same executor.

How to use this executor?

Choose a runtime, open or create a file, write your code, and select Run. Output appears in the terminal, while signed-in users can keep files in a workspace, install libraries, and collaborate through shares.

  1. Select a version and edit the current file or open another workspace file.
  2. Run the code, provide input in the terminal when requested, and review saved run history.
  3. Use libraries, workspace tools, sharing, and chat when your task needs more than one snippet.

💡 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();