Runnable.java

class MyRunnable implements Runnable {
  
  // Create class properties we can set
  private String message;

  // Create Constructor - can customise 
  // what's set when we create a new instance
  public MyRunnable(String message) {
    // Set class properties y
    // when we create the a new instance of the class
    this.message = message;

  }

  //  We must implement this function
  //  Because the Runnable interface requires it to exist
  //  Java would error on compile if we didn't
  public void run() {
    // Do something in a thread
    println this.message
  }

}

public class RunnableExample {
  public static void main(String[] args) {

    // Initialise a variable of Type Runnable
    // and Instantiate new MyRunnable class instance
    Runnable r1 = new MyRunnable("I can run");

    // Initialise a variable of Type Thread
    // and Instantiate a new Thread class instance
    // Passing in our custom runnable
    Thread t1 = new Thread(r1);

    // Execute our Thread by calling the start function.
    t1.start();

  }
}