线程“DoorLock”中的异常 java.lang.NullPointerException

Question

hello the program complies but when the program runs it shows this error then carries on displaying the threads etc the format on this post took so long to post.... 1 2 3 4 5 6 7 8 9 10 11 12 13412414145256t423626262626263573

Exception in thread "DoorLock" java.lang.NullPointerException
    at miniass3.AirlockDoor.run(AirlockDoor.java:15)
    at java.lang.Thread.run(Unknown Source)"

Here is my code:

package uk.ac.aber.dcs.airlock;
import miniass3.AirLock;
import miniass3.AirlockDoor;

public  class AstronautSimulator {

    public static void main(String [] args){
        simulate();
    }

    private  static void simulate() {
        // Create an AirLock object
        // STEP 1: CREATE AN EMPTY VERSION OF THE AirlockDoor CLASS
        AirlockDoor[] doors = new AirlockDoor[2];

        // For this prototype this can be an empty (no method)
        // class. It is a common object used in the Door class
        // that contains the single lock-key that protects the
        // imaginary airlock room from having two doors open at
        // the same time
        // STEP 2: CREATE THIS CLASS
        AirLock MainAirLock = new AirLock();

        // Give the doors a name (for debugging purposes) and
        // a common airlock object used to store the "key" used
        // by a critical section of code in the Door class   
        doors[0] = new AirlockDoor("Door 1", null);
        doors[1] = new AirlockDoor("Door 2", null);

        // AirlockDoor implements Runnable and so make sure
        // we tie the objects to Thread objects
        Runnable threadJob = new AirlockDoor(null, MainAirLock);

        // STEP 3: CREATE TWO THREADS FOR THE TWO DOORS AND START THEM
        // ENTER CODE HERE
        Thread doorController1 = new Thread(threadJob);
        // Thread doorController2 = new Thread(threadJob);
        doorController1.setName("DoorLock");
        //doorController2.setName("DoorLock");
        doorController1.start();
        // doorController2.start();

        // Loop infinitely which try's to open the airlock doors
        while (true) {
            // random() returns a value in range 0.0..<1.0 multiplied by 10 and  mod doors.length
            // to return either 0 or 1 in order to randomly decide which door to request
            int doorNum = (int)((Math.random() * 10) % doors.length);

            // STEP 4: MAKE A REQUEST TO OPEN THE DOOR AND THEN ADD A DELAY    BEFORE
            // TRYING TO OPEN ANOTHER DOOR
            // ENTER CODE HERE
            doors[doorNum].requestToOpen();
            try{
                Thread.sleep(800);
            } catch(InterruptedException ex) {
                ex.printStackTrace();
            }
        }
    }
}

Separate:

package miniass3;
public  class AirlockDoor implements Runnable {
    private AirLock lockOperator;
    private String doorName;
    // private boolean Door1OpenRequest = false; 
    //private boolean Door2OpenRequest = false;  
    public AirlockDoor(String doorName, AirLock airLock) {
        this.doorName = doorName;
    }

    public void run() {    
        while (true) {
            //this is the line that fails
            if(lockOperator.isLockState() == false); {
                System.out.println("False");
            }            
        }
    }

    public  void  requestToOpen() {
        System.out.println(doorName +  " requests to be opened");
    }
}

sperate

 package  miniass3;
 public class AirLock {

    private boolean lockState = false;
    // TODO: Change this to look like setLockState method.
    public  void setAirLock(boolean newLock) {
        this.lockState = newLock;
    }

    public  boolean isLockState() {
        return lockState;
    }

    public void setLockState(boolean lockState) {
        this.lockState = lockState;
    }
}

Answer 1

lockOperator is not initialized. But you are trying to access the lockOperator.

public AirlockDoor(String doorName, AirLock airLock)
{
    this.lockOperator = airLock; // you missed to assign the airLock to lockOperator. So that the lockOperator is not yet assigned
    this.doorName = doorName;
}

instead of

public AirlockDoor(String doorName, AirLock airLock)
{
    this.doorName = doorName;
}