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author: ["MaritvanDijk"]

<a id="overview">&nbsp;</a>

One of the [most widely used integrated development environments (IDEs)](https://www.jetbrains.com/lp/devecosystem-2023/java/#java_ide) for Java is IntelliJ IDEA. Its user-friendly interface, rich feature set, and vast ecosystem make it an ideal environment for beginners to learn and grow as developers. In this tutorial you’ll learn how to use some of its features to simplify your development process and accelerate your learning curve with Java programming.

We can see the project structure in the [Project tool window](https://www.jetbrains.com/help/idea/project-tool-window.html) on the left. The `.idea` folder contains your project configuration. The `src` folder contains your code. When you expand that folder, you'll see that IntelliJ IDEA has created a `main` folder for your Java code and a `test` folder for your tests.

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public static void main(String[] args) {

}

public static void main(String[] args) {

[](/assets/images/intellij-idea/alt-enter.png)

[](/assets/images/intellij-idea/generate-code.png)

A major benefit of using an IDE is that you can directly run your code without having to first manually compile it on the command line.

Alternatively, we can run our application using the green Run button in the top right corner, or using the shortcut **⌃R** (on macOS) or **Ctrl+F10** (on Windows/Linux) to run the latest file.

[](/assets/images/intellij-idea/edit-configurations.png)

[](/assets/images/intellij-idea/run-config.png)

<a id="test">&nbsp;</a>

Testing your code helps you to verify that the code does what you expect it to do. You can run your application and test it yourself, or add automated tests that can verify your code for you. Thinking about what to test and how, can help you to break a problem up into smaller pieces. This will help you get a better solution faster!

int sum = 0;

for (int number : numbers) {

sum += number;

Note that the JUnit 5 dependency `junit-jupiter` is added to the `pom.xml` in the `<dependencies>` section.

Go back to the test file to add tests. We can let IntelliJ IDEA help us generate our test for us. In the test class, we can use **Generate** (**⌘N** on macOS or **Alt+Insert** on Windows/Linux) and select **Test Method** to add a test. Give the test a name that explains the intended behavior, and add the relevant test code.

import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertEquals;

@Test

void shouldCalculateAverageOfPositiveNumbers() {

int[] numbers = {1, 2, 3, 4, 5};

double expectedAverage = 3.0;

assertEquals(expectedAverage, actualAverage);

void shouldReturnZeroAverageForEmptyArray() {

int[] numbers = {};

double expectedAverage = 0;

assertEquals(expectedAverage, actualAverage);

Execution will stop at the breakpoint, so we can investigate the state of our application. We can see current values of variables and objects. We can evaluate an expression, to see its current value and look at more details. We can even change the expressions to evaluate different results. We can continue execution by either stepping into a method to see what happens inside a called method (using the shortcut **F7**, or the corresponding button in the *Debug* tool window) or stepping over a line to go to the next line even if a method is called (using the shortcut **F8**, or the corresponding button in the *Debug* tool window), depending on what we’re interested in. Finally, we can resume the program to finish the execution of the test.

[](/assets/images/intellij-idea/debug.gif)

if (numbers.length == 0) {

return 0;

}

<a id="refactor">&nbsp;</a>

Pull up the refactoring menu to see what is possible, using the shortcut **⌃T** (on macOS) or **Ctrl+Alt+Shift+T** (on Windows/Linux).

We can add documentation to our code. IntelliJ IDEA provides completion for documentation comments, which is enabled by default. Type `/**` before a declaration and press **Enter**. IntelliJ IDEA auto-completes the documentation comment for you.

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