Error in run() method when using Thread.sleep()

Question

I am trying to run an Elevator instance in its own thread. The run() method is being called, but there must be some error in my code that is preventing it from running. My code compiles and runs without errors, but the "Elevator starting up" is never printed.

I think it has to do with Thread.sleep() needing to throw an InterruptedException. I tried to try/catch the exception since Runnable doesn't throw an InterruptedException.

Can you help me figure out why it isn't running?

Here is my run() method:

@Override
public void run() {
    System.out.printf("Elevator starting up");

    while(true) {
        try {
            if (currentDirection == Direction.UP) {
                this.moveUp();
            }
            else if (currentDirection == Direction.DOWN) {
                this.moveDown();
            }
            else {Thread.sleep(250);}
        }
        catch (InterruptedException ie) {
            System.out.println("Elevator has experienced a critical error")
        }
    }
}

Here is my start() method within the Elevator class. This is called from main for each elevator in the building.

public void start() {
    activeThread = new Thread();
    activeThread.start();
}

The moveUp() method:

public void moveUp() throws InterruptedException {
    Thread.sleep(travelSpeed);
    setCurrentFloor(currentFloor++);
}

The moveDown() method:

public void moveDown() throws InterruptedException{
    Thread.sleep(travelSpeed);
    setCurrentFloor(currentFloor--);
}

Full PassengerElevator.class code

public class PassengerElevator implements ElevatorMover, Runnable {

private final int elevID;       // elevator number
private final int maxCapacity;  // max capacity of the elevator
private int currentCapacity;    // the current capacity of the elevator
private final long travelSpeed; // length of travel time between floors
private final long doorSpeed;   // length of time door stays open
private int currentFloor;       // the current floor the elevator is on
private final int defaultFloor; // the default floor after timeout
private Direction currentDirection; // the current direction the elevator is moving
public Thread activeThread = null;  // contains the instance of an elevator thread

/**
 * Constructor
 * @param elevID the ID number, as an int, given to the elevator
 */
public PassengerElevator(int elevID) {

    this.elevID = elevID;
    maxCapacity = 10;
    currentCapacity = 0;
    travelSpeed = 500;  // in milliseconds
    doorSpeed = 500;    // in milliseconds
    currentFloor = 1;
    defaultFloor = 1;
    currentDirection = Direction.IDLE;
}

/**
 * makes the elevator go up one floor. Takes travelSpeed time
 * @throws InterruptedException 
 */
@Override
public void moveUp() throws InterruptedException {
    Thread.sleep(travelSpeed);
    setCurrentFloor(currentFloor++);
}

/**
 * makes the elevator go down one floor. Takes travelSpeed time
 * @throws InterruptedException 
 */
@Override
public void moveDown() throws InterruptedException{
    Thread.sleep(travelSpeed);
    setCurrentFloor(currentFloor--);
}

/**
 * makes the elevator door open for doorSpeed time. When door is open people
 * move into elevator
 * @throws InterruptedException 
 */
@Override
public void openDoors() throws InterruptedException{
    Thread.sleep(doorSpeed);
}

public int getElevID() {
    return elevID;
}

private int getMaxCapacity() {
    return maxCapacity;
}

private int getCurrentCapacity() {
    return currentCapacity;
}

private void setCurrentCapacity(int x) {
    currentCapacity = x;
}

private double getTravelSpeed() {
    return travelSpeed;
}

private double getDoorSpeed() {
    return doorSpeed;
}

public int getCurrentFloor() {
    return currentFloor;
}

private void setCurrentFloor(int x) {
    currentFloor = x;
}

private int getDefaultFloor() {
    return defaultFloor;
}

private void setCurrentDirection(Direction x) {
    currentDirection = x;
}

private Direction getCurrentDirection() {
    return currentDirection;
}

/**
 * Starts a new thread for an elevator instance to run in
 */
public void start() {
    activeThread = new Thread();
    activeThread.start();
}

/**
 * The running loop for an elevator instance. Client will change current direction
 * and use the currentFloor as a check.
 */
@Override
public void run() {
    System.out.printf("Elevator starting up");

    while(true) {
        try {
            if (currentDirection == Direction.UP) {
                this.moveUp();
            }
            else if (currentDirection == Direction.DOWN) {
                this.moveDown();
            }
            else {Thread.sleep(250);}
        }
        catch (InterruptedException ie) {
            System.out.println("Elevator has experienced a critical error")
        }
    }

}

}

@Kon, it compiles, but I'm never getting "Elevator starting up" on my console — clenard, Feb 10 '15 at 15:48
@DavidGrinberg it runs, but I'm never getting "Elevator starting up" on my console — clenard, Feb 10 '15 at 15:48
You're never running your run() method. You start a new Thread but don't schedule anything on it. — Adrian Leonhard, Feb 10 '15 at 15:48
I dont see you ever actually change the direction in your code. — David says Reinstate Monica, Feb 10 '15 at 15:50
@AdrianLeonhard I was under the impression that Thread.start() did that for you. — clenard, Feb 10 '15 at 15:51
@clenard It runs its own run() method which is by default empty. Either have Elevator extends Thread and then do new Elevator(). Or Elevator extends Runnable and do new Thread(new Elevator()). — Adrian Leonhard, Feb 10 '15 at 15:52
@Thecazziator33 Isn't that what my start() method is doing. I thought it was creating a new Thread object and then starting it. — clenard, Feb 10 '15 at 15:52
`activeThread = new Thread();` should most probably be something like `activeThread = new ElevatorThread();` or `activeThread = new Thread(myElevatorRunnable);` — Keppil, Feb 10 '15 at 15:53
@DavidGrinberg Do I have to change the direction to make it run? I just want the run method to start running in the infinite loop until I tell the elevator to change direction with my Elevator Control System — clenard, Feb 10 '15 at 15:54
I never see you set the direction in the first place. Can you post the `Elevator` code? — David says Reinstate Monica, Feb 10 '15 at 15:55
Where is the run() mehod? With `activeThread = new Thread();` and `activeThread.start();` you are just initializing and starting a new thread... I think we need more code... — Marcello Davi, Feb 10 '15 at 15:57
How do you change direction? you start at idle ... and remain there. — Roddy of the Frozen Peas, Feb 10 '15 at 16:00
@TheCazziator33 I have added the full code for PassengerElevator above. My start() and run() are near the bottom. — clenard, Feb 10 '15 at 16:00
@RoddyoftheFrozenPeas I am having the elevator sit in an Idle position until my ElevatorController system receives a request from a person and tells the elevator to go Up or Down — clenard, Feb 10 '15 at 16:02

score 3 · Accepted Answer · answered Feb 10 '15 at 15:58

You are creating a Thread instance directly, and since it is the plain Java Thread class, it has no code in the run method. That means that when you start it, it does nothing. This is the relevant code:

public void start() {
    activeThread = new Thread();
    activeThread.start();
}

You need to start a thread that is going to run your code. Either make your elevator class extend Thread or implement Runnable.

When extending Thread:

thread = new Elevator();
thread.start();

When implementing Runnable:

thread = new Thread(new Elevator());
thread.start();

The Thread documentation provides examples of usage.

This solves my question. Unfortunately, it means I've been barking up the wrong tree. haha. Learning pains. — clenard, Feb 10 '15 at 16:07

Error in run() method when using Thread.sleep()

1 Answers1