Runnable

Learn to define tasks with Runnable.

Runnable

Runnable is the interface that represents a thread task. Instead of extending Thread, you implement Runnable; this gives flexibility for classes that already extend another class.

class PrintTask implements Runnable {
    public void run() {
        System.out.println("Running");
    }
}

Thread t = new Thread(new PrintTask());
t.start();

Since Java 8 a lambda is shorter: new Thread(() -> System.out.println("Hi")). This is the preferred functional style. Runnable returns no result; use Callable for a result.

Runnable with lambda

Since Java 8 a Runnable can be written as a lambda. With a single abstract method (run), the compiler maps it automatically.

Runnable r = () -> System.out.println("Hi");
new Thread(r).start();

This is much shorter than writing an anonymous class. The @FunctionalInterface annotation marks the interface as having a single abstract method; this makes lambda use safe. Modern Java code prefers lambdas.

Exercise Implement Runnable with PrintTask

Define a PrintTask class that implements the Runnable interface; in public void run() call System.out.println("Task running"). In a RunnableDemo class write main; create an instance of PrintTask and call run() directly.

Show example solution

class PrintTask implements Runnable {
    public void run() {
        System.out.println("Task running");
    }
}

class RunnableDemo {
    public static void main(String[] args) {
        new PrintTask().run();
    }
}

Test yourself

Complete the Runnable implementation

class PrintTask implements ____ {
    public void run() {
        System.out.println("Çalışıyor");
    }
}

Show answer

class PrintTask implements Runnable {
    public void run() {
        System.out.println("Çalışıyor");
    }
}

What is the name of Runnable's single abstract method?
- call()
- apply()
- get()
- run()
Show answer

run() — Runnable's single method is run().
Match the task interfaces

Runnable

Returns no result
Callable

Returns a result
Thread

Represents a thread
@FunctionalInterface

Marks a single abstract method

Next lesson: start and join

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies