Online Java Compiler

Write, compile, run, and debug Java code online in a full-featured browser IDE. Work with multiple files, save your workspace, and share or collaborate in real time - no setup required.

Version

Pre-installed Libs

🚀 257,389 total executions (2,835 this month)

Output

Practice Python with coding challenges

Solve hands-on problems right in this editor: run the sample tests, submit, and get an AI code review.

All Python challenges

Easy

Rectangle Perimeter

Compute the perimeter of a rectangle from its sides.

You'll learn ArithmeticReturn values

BeginnerLearning-pathVariables

View solutions (6)

Easy

Days in a Month

Return how many days a month has, including leap years.

You'll learn Calendar rulesHelper functions

BeginnerConditionsFunctionsLearning-path

View solutions (3)

Easy

Dot Product of Two Vectors

Multiply two vectors element by element and add the results: the core operation of every neuron.

You'll learn VectorsDot product

Neural networksaimachine learning

View solutions (3)

Easy

Distance Between Points

Compute the straight-line distance between two points.

You'll learn Pythagorean theoremSquare roots

BeginnerFunctionsLearning-pathmath

View solutions (2)

Easy

Average of Three

Average three whole numbers.

You'll learn ArithmeticDivision

BeginnerLearning-pathVariables

View solutions (2)

Easy

To-Do List

Keep a list of tasks: add them, mark them done, remove them and report what is still pending.

You'll learn Typed collectionsRecords

BeginnerSimulationStrings

View solutions (1)

Easy

Prime Number Check

Decide whether a number is prime.

You'll learn DivisibilityLoop optimization

BeginnerLoopsNumbersStudent-beginner

View solutions (1)

Hard

Word Break

Decide whether text can be split into dictionary words.

You'll learn Prefix DPString segmentation

AdvancedDynamic-programmingHackathonStrings

View solutions (1)

Easy

Count Pairs With a Sum

Count pairs of positions whose values add up to a target.

You'll learn Pairs of indexesAvoiding double counts

ArraysBeginnerLearning-pathNested-loops

View solutions (1)

Easy

Missing Number

Find the one number missing from 0..n.

You'll learn Arithmetic seriesSum difference trick

ArraysBeginnerStudent-beginnermath

View solutions (1)

Medium

K-th Smallest Element

Find the k-th smallest value without fully sorting.

You'll learn QuickselectPartitioning

AdvancedCompetitive-programmingSorting

View solutions (1)

Easy

Min and Max Together

Find the smallest and largest value in one pass.

You'll learn Single passMultiple return values

ArraysBeginnerFunctionsLearning-path

View solutions (1)

☕ 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.

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

Start coding

VersionSelect a runtime before running. Installed libraries belong to the selected language version.
Open files lists unopened text files. Select one to open it in an available editor tab.
Run executes the active file with its workspace available to the program.
Stop ends the current execution before its time limit.
Advanced Mode opens the IDE layout with a file explorer and movable, resizable terminal.

Workspace and libraries

New file creates a file in the selected parent directory and opens it in the editor.
New folder creates a directory, up to the supported nesting depth.
Upload files adds one or more safe files to a directory.
Download saves a file or a zipped directory to your device.
Copy duplicates a workspace file or directory.
Rename changes a file name and updates its open tab and history.
Move relocates an item; files and directories can also be dragged.
Delete removes an item after confirmation and closes its open editor tab.
Pre-installed Libs shows packages already included in this runtime.
Add Lib installs a private package for your account and selected runtime.

Terminal and assistance

Run history opens previous and next saved outputs.
Copy output copies the current terminal text.
Clear output removes all saved run outputs after confirmation.
Explain summarizes the active code.
Recents opens recent explanations and results.
Settings changes fonts, themes, and visible toolbar buttons.

Sharing and collaboration

Share publishes the current file, a directory, or the whole workspace as a snapshot or live workspace. You control link access and who may save changes.
Logs records saved collaborator actions in a shared workspace.
Share chat lets signed-in participants message, mention people, share code blocks, and see online or typing members.
Live collaboration shows collaborator cursors and saved file updates. View-only users can load the latest version or keep temporary edits.

Quotas and limits

Execution time is limited to 20 seconds per server run. Use Stop when you want to end it sooner.
Workspace storage allows 100 files, 100 directories, and 10 MiB total for each signed-in user workspace and language.
Files and folders are limited to 1 MiB per file and 5 nested directory levels. Files generated by your code follow the same quota.
Private libraries are limited to 10 installed packages for each account and runtime.
Share snapshots can contain up to 100 files, 1 MiB per file, and 2 MiB total.
Share invitations support up to 25 people per share, with access and saving permissions managed separately.
Share chat allows 2,000 characters per message and 10,000 messages per share.
Quota enforcement also applies while code is running. A write that exceeds file count, size, storage, or nesting limits is rejected safely.

Good to know Only run code and install packages you trust. Execution is isolated and limited, but your program can still modify files inside a writable workspace up to its enforced quota.

💡 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();