# Java examples
<a name="examples-java"></a>

The following Java examples demonstrate how users can get started in generating in-line code suggestions. These illustrative examples show you how to trigger the coding assistant for your own projects. A majority of the following examples are applicable to other languages: 
+ [Generate classes and functions](#classes-java)
+ [Document code](#code-java)
+ [Generate algorithms](#algorithms-java)
+ [Generate unit tests](#tests-java)

## Generate classes and functions
<a name="classes-java"></a>

To generate full or partial class implementation, use code comments. The comment describes the intention of the class. Start simple, and add more details if necessary. After you generate a class, you can continue to generate functions within its skeleton. 

When writing comments, it's preferable to use the language's comment structure. In Java, this is `/** */`*.* 

Input: 

```
/**
 * DocumentReader class. has a name, children and optional parent. 
 * Includes I/O functions to read and
 * write document
 */
```

Output: 

```
/**
 * DocumentReader class. has a name, children and optional parent. 
 * Includes I/O functions to read and
 * write document
 */
import java.util.ArrayList;
public class DocumentReader {
    private String name;
    private DocumentReader parent;
    private ArrayList<DocumentReader> children;

    /**
     * Constructor
     * @param name name of the document
     * @param parent parent of the document
     */
    public DocumentReader(String name, DocumentReader parent) {
        this.name = name;
        this.parent = parent;
        this.children = new ArrayList<>();
    }

    /**
     * Constructor
     * @param name name of the document
     */
    public DocumentReader(String name) {
        this(name, null);
    }
    /**
     * Getter for name
     * @return name of the document
     */
    public String getName() {
        return name;
    }

    /**
     * Getter for parent
     * @return parent of the document
     */
    public DocumentReader getParent() {
        return parent;
    }

    /**
     * Getter for children
     * @return children of the document
     */
    public ArrayList<DocumentReader> getChildren() {
        return children;
    }

    /**
     * Adds a child to the document
     * @param child child to be added
     */
    public void addChild(DocumentReader child) {
        children.add(child);
    }

    /**
     * Removes a child from the document
     * @param child child to be removed
     */
    public void removeChild(DocumentReader child) {
        children.remove(child);
    }
}
```

Now that there is an initial class, an additional function can be generated with additional comments. 

Input:

```
/**
* function to read document from local directory path
* and print first line of document
*/
```

Output:

```
/**
 * function to read document from local directory path
 * and print first line of document
 */
public void readDocument() {
    try {
        BufferedReader reader = new BufferedReader(new FileReader(name));
        String line = reader.readLine();
        System.out.println(line);
        reader.close();
    } catch (IOException e) {
        System.out.println("Error reading document: " + e.getMessage());
    }
}
```

## Document code
<a name="code-java"></a>

Reduce time in code documentation by relying on in-line documentation. Add a Java comment break `/* */`.

Input: 

```
import java.util.function.Function;

public class S3Utils {
    /* 
     * <place cursor here>
    */
    public static Function<String, String> generateS3Function(String bucketName, String region) {
        return (String key) -> {
            String url = generateS3Url(bucketName, key, region);
            return url;
        };
    }
}
```

If in-line generation doesn't occur, execute an Amazon Q Developer in-line suggestion after placing your cursor where you want documentation.

Output:

```
import java.util.function.Function;

public class S3Utils {
    /* 
     * Generate a function that returns the S3 URL for a given key
     * @param bucketName the name of the bucket
     * @param region the region of the bucket
     * @return the function that generates the S3 URL
    */
    public static Function<String, String> generateS3Function(String bucketName, String region) {
        return (String key) -> {
            String url = generateS3Url(bucketName, key, region);
            return url;
        };
    }
}
```

For simpler explanations of code (classes, functions, or script elements), use forward characters (`//`)that are strategically placed before code sections where you want to add documentation. 

Input:

```
// 
public class S3Utils {
    /* 
     * Generate a function that returns the S3 URL for a given key
     * @param bucketName the name of the bucket
     * @param region the region of the bucket
     * @return the function that generates the S3 URL
    */
    public static Function<String, String> generateS3Function(String bucketName, String region) {
        return (String key) -> {
            String url = generateS3Url(bucketName, key, region);
            return url;
        };
    }
}
```

Output:

```
// This class is used to generate a function that returns the S3 URL for a given key
public class S3Utils {
    /* 
     * Generate a function that returns the S3 URL for a given key
     * @param bucketName the name of the bucket
     * @param region the region of the bucket
     * @return the function that generates the S3 URL
    */
    public static Function<String, String> generateS3Function(String bucketName, String region) {
        return (String key) -> {
            String url = generateS3Url(bucketName, key, region);
            return url;
        };
    }
}
```

## Generate algorithms
<a name="algorithms-java"></a>

Amazon Q Developer can generate popular algorithms, especially related to AWS SDKs. In your script, add a prompt that specifies the function you want. 

This example generates a hash map of user id keys to name values and then generates a sorting function using the bubble sort algorithm.

Input:

```
import java.util.HashMap;
public class SortList {

    // generate key value pair hash map for 
    // user id and name
    public static HashMap<Integer, String> getUserIdNameMap() {
        HashMap<Integer, String> userIdNameMap = new HashMap<Integer, String>();
        userIdNameMap.put(1, "Amit");
        userIdNameMap.put(2, "Rahul");
        userIdNameMap.put(3, "Vijay");
        userIdNameMap.put(4, "Raj");
        userIdNameMap.put(5, "Kumar");
        return userIdNameMap;
    }

    /*
    * Create function to sort UserIdName map by name alphabetically using bubble sort
    */ 
    
    
}
```

Output:

```
/*
* Create function to sort UserIdName map by name alphabetically using bubble sort
*/ 
public static HashMap<Integer, String> sortUserIdNameMap(HashMap<Integer, String> userIdNameMap) {
    int size = userIdNameMap.size();
    for (int i = 0; i < size; i++) {
        for (int j = i + 1; j < size; j++) {
            if (userIdNameMap.get(i).compareTo(userIdNameMap.get(j)) > 0) {
                String temp = userIdNameMap.get(i);
                userIdNameMap.put(i, userIdNameMap.get(j));
                userIdNameMap.put(j, temp);
            }
        }
    }
    return userIdNameMap;
}
```

In addition, users can create prompts for standard procedures. In this example, the user creates a prompt to store the hash map to an Amazon DynamoDB table. At the beginning of the script, the user adds a prompt to add DynamoDB Java libraries to help provide Amazon Q Developer with additional context.

Input:

```
// add libraries for Amazon DynamoDB
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;

     /*
     * Store sorted UserIdName map into Amazon DynamoDB table named users
     */
```

Output:

```
// add libraries for Amazon DynamoDB
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;

     /*
     * Store sorted UserIdName map into Amazon DynamoDB table named users
     */
    public static void storeSortedUserIdNameMap(HashMap<Integer, String> userIdNameMap) {
        // create Amazon DynamoDB client
        AmazonDynamoDB client = AmazonDynamoDBClientBuilder.defaultClient();

        // store sorted UserIdName map into Amazon DynamoDB table named users
        for (int userId : userIdNameMap.keySet()) {
            String name = userIdNameMap.get(userId);
            client.putItem("users", new HashMap<String, Object>() {{
                put("userId", userId);
                put("name", name);
            }});
        }
    }
```

## Generate unit tests
<a name="tests-java"></a>

With in-line comments, Amazon Q Developer can generate unit tests to perform assertions and other JUnit tests. In this example, the user first asks Amazon Q to generate applicable libraries for JUnit to set the context of the test script. Next, the user creates a public class followed by a declarator and comment strings.

Input:

```
// import libraries for java unit tests
import org.junit.Test;
import static org.junit.Assert.*;

public class UnitTests {

    @Test 
    /*
     * Create unit test for getUserIdNameMap
     */  
}
```

Output:

```
@Test 
/*
* Create unit test for getUserIdNameMap
*/
public void testGetUserIdNameMap() {
    // create a new instance of the UserIdNameMap class
    UserIdNameMap userIdNameMap = new UserIdNameMap();

    // create a new instance of the User class
    User user = new User("John", "Doe");

    // add the user to the map
    userIdNameMap.addUser(user);

    // get the user from the map
    User retrievedUser = userIdNameMap.getUser("John");

    // assert that the retrieved user is the same as the user added to the map
    assertEquals(user, retrievedUser);
}
```

In addition, in a chat between the user and Amazon Q Developer, it suggests and generates unit tests based on the user's code input prompts. For more information, see [Chat examples](examples-chat.md).