import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

class AppTest {
    @Test void appHasAGreeting() {
        App classUnderTest = new App();
        assertNotNull(classUnderTest.getGreeting(), "app should have a greeting");
    }

package org.gradle.sample;

import java.io.InputStream;
import org.apache.log4j.LogManager;

public class Greeter {
    public String getGreeting() throws Exception {
        LogManager.getRootLogger().info("Just checking if we can use external dependencies....");
        return "hello Gradle";
    }

package org.gradle.sample;

import java.io.InputStream;
import org.apache.log4j.LogManager;
import org.apache.commons.io.IOUtils;

public class Greeter {
    public String getGreeting() throws Exception {
        LogManager.getRootLogger().info("generating greeting.");
        InputStream greetingStr = getClass().getResourceAsStream("/greeting.txt");
        try {
            return IOUtils.toString(greetingStr).trim();
        }
        finally {

            }
        """

        and: "containing a class to compile"
        file("src/main/java/org/test/App.java") << """
            public class App {
                public String getGreeting() {
                    return "Hello World!";
                }
            }
        """

        and: "containing a test"
        file("src/test/java/org/test/MyTest.java") << """

            public class App {
                public String getGreeting() {
                    return new Producer().sayHello("Stranger");
                }

                public static void main(String[] args) {
                    System.out.println(new App().getGreeting());
                }
            }
        """

        createDirs("producer")

.App.java
[source, java]
----
package authoring.tutorial;

public class App {
    public String getGreeting() {
        return "Hello World!";
    }

    public static void main(String[] args) {
        System.out.println(new App().getGreeting());
    }
}
----

The code prints out a simple "Hello World" greeting to the screen.

The Java code in `App.java` simply prints "Hello World" to the screen:
[source,java]
----
public class App {
    public String getGreeting() {
        return "Hello World!";
    }
    public static void main(String[] args) {
        System.out.println(new App().getGreeting());
    }
}
----

[.text-right]

[source,java]
----
package authoring.tutorial;

import com.gradle.CustomLib;

public class App {
    public String getGreeting() {
        return "CustomLib identifier is: " + CustomLib.identifier;
    }

    public static void main(String[] args) {
        System.out.println(new App().getGreeting());
    }
}
----

Finally, let's run the `app` with the command `./gradlew run`:

[source]
----

            @DisableCachingByDefault(because = "test task")
            abstract class MyTask extends DefaultTask {

                @Input
                @Optional
                abstract Property<String> getGreeting();

                @Input
                Provider<String> message = greeting.map(it -> it + " from Gradle");

                @TaskAction
                void printMessage() {

                    return "Hello!"
                }
            }

            abstract class MyTask extends DefaultTask {
                @Input
                abstract Property<String> getGreeting()

                @TaskAction void run() { println greeting.get() }
            }

            def greetValueSource = providers.of(GreetValueSource) {}
            tasks.register("greet", MyTask) {