Online Java Code Editor for Interviews

Getting Started with Our Java Code Editor

In CodeInterview, you have the flexibility to work with Java in the way that best suits your needs. If you want to conduct an interview with a direct coding challenge, we offer a single-file Java environment. However, for a more comprehensive and realistic interview, we provide a multi-file Java project environment. Learn more below.

Single-file Java Environment

The single-file Java environment simplifies technical interviews by focusing on core programming skills and quick problem-solving tasks.

This environment runs OpenJDK 21, powered with Intellisense.

You should define public static void main(java.lang.String[]) inside a public class.

We have added both JUnit 4 and JUnit 5 for your convenience. Because this is a single-file environment, you run your test suite straight from main() using each framework's runner. Make sure your main class is public and named Code.

Using JUnit 4, call JUnitCore from main():

import org.junit.*;
import org.junit.runner.*;

public class Code {
    @Test
    public void testNoop() {
        Assert.assertTrue(true);
    }

    public static void main(String[] args) {
        JUnitCore.main("Code");
    }
}

Using JUnit 5, launch the suite through the JUnit Platform Launcher from main():

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.platform.launcher.*;
import org.junit.platform.launcher.core.LauncherFactory;
import org.junit.platform.launcher.listeners.SummaryGeneratingListener;
import static org.junit.platform.engine.discovery.DiscoverySelectors.selectClass;
import static org.junit.platform.launcher.core.LauncherDiscoveryRequestBuilder.request;

public class Code {
    @Test
    public void testNoop() {
        assertTrue(true);
    }

    public static void main(String[] args) {
        LauncherDiscoveryRequest req = request()
            .selectors(selectClass(Code.class)).build();
        Launcher launcher = LauncherFactory.create();
        SummaryGeneratingListener listener = new SummaryGeneratingListener();
        launcher.registerTestExecutionListeners(listener);
        launcher.execute(req);
        listener.getSummary().printTo(new java.io.PrintWriter(System.out));
    }
}

Single-file Java environment comes with the following installed Libraries:

• JUnit 4 and JUnit 5 - These are among the best test automation frameworks for the Java programming language. You can use JUnit as mentioned above to assess the Unit Testing skills of your candidate.
• Apache Commons Lang - This library provides various helper utilities for the java.lang API. Like, String manipulation methods, object reflection, basic numerical methods, concurrency, creation and serialization and System properties.
• JSON-Simple - This library is used for encode or decode JSON text.You can also do the streaming output of JSON text.

This code is compiled using the -XLint option.

Multi-file Java Project Environment

The multi-file Java environment enhances technical interviews by accommodating complex, real-world coding scenarios and project-based assessments. It's ideally suited for in-depth evaluations, allowing candidates to demonstrate their ability to architect software, manage multiple files, and integrate various components seamlessly.

This environment runs OpenJDK 21, powered with Intellisense.

This environment comes ready with Maven. Using the pom.xml file and the interactive shell, you can prepare your interviews with certain libraries as per your needs.

Just like single-file environments, there are some basic libraries already installed with this environment as they can be seen in the pom.xml file:

• Apache Commons Lang - A utility library for Java, enhancing the default language features.
• Logback Classic - A robust logging framework for Java applications, part of the Logback family.
• SLF4J API - A simple facade for various logging frameworks (like Logback), allowing the end user to plug in the desired logging framework at deployment time.

Code is executed using the mvn compilecommand.

Amazing Candidate Experience

At CodeInterview, our Java Online IDE and Code Editor enhance candidate experiences by offering both single-file and multi-file options. This flexibility allows candidates to efficiently showcase their skills in a user-friendly environment, ensuring a seamless and delightful interview process.