Java Null Pointer Exception when creating new instance of class

Question

I'm in my first year of computer science and am having a hell of a time with a project. I was given the code that creates a list of room numbers via an array, and I am to create a method that allows the user to pick a room, enter in their information, and reserve the room.

My issue seems to lie in creating the method that actually reserves the room... which is as follows...

 public void bookRoom (Room[] room, int numberOfRooms)
{

    //Get settings for room (smoking, occupied, guest name/number)

    displayRoomsInfo(room, numberOfRooms);

        Room room1 = new Room(false, false, null, null, numberOfRooms);



    //user input,store each value to temp variables

    Scanner scan=new Scanner(System.in);
    System.out.println("Please choose a room");

    int guestRoomNum=scan.nextInt();
    room1.setRoomNumber(guestRoomNum);

    //set room[i] occupied = true;

    room1.setOccupied(true);

    //set room[i] guestname to name

    System.out.println("Enter Guest Name");
    String dickshit = scan.next();
    String[] nameList = {dickshit};
    room1.setGuestName(nameList);



    //set room[i] guestnumber to phone

    System.out.println("Enter Guest Phone Number");
    String phoneInput = scan.next();
    room1.setGuestPhone(phoneInput);
    }

I keep getting a null pointer exception on

Room room1 = new Room(false, false, null, null, numberOfRooms);

Which is the line where I actually create an instance of the custom class that I was provided. I don't have a freaking clue as to why or how I can go about preventing this, since those appear the default constructor values.

The Room class code is as follows:

public class Room {

private boolean smoking;
private boolean occupied;
private String[] guestName=new String[4];
private String guestPhone;
private int roomNumber;

public Room (boolean smoking,boolean occupied,String[] guestName, String guestPhone,int roomNumber)
{
    this.smoking=smoking;
    this.occupied=occupied;
    for (int i=0;i<4;i++)
        this.guestName[i]=guestName[i];
    this.guestPhone=guestPhone;
    this.roomNumber=roomNumber;

}
public void setGuestName(String[] guestName)
{
    for (int i=0;i<4;i++)
        this.guestName[i]=guestName[i];
}


public String[] getGuestName()
{
    String[] tempGuestName=new String[4];
    for (int i=0;i<4;i++)
        tempGuestName[i]=this.guestName[i];
    return tempGuestName;
}

public void setOccupied(boolean isFull)
{
    this.occupied=isFull;
}

public boolean getOccupied()
{
    return occupied;
}


public void setSmoking(boolean canSmoke)
{
    this.smoking=canSmoke;
}

public boolean getSmoking()
{
    return smoking;
}


public void setGuestPhone(String phoneNumber)
{
    this.guestPhone=phoneNumber;
}

public String getGuestPhone()
{
    return guestPhone;
}


public void setRoomNumber(int roomNum)
{
    this.roomNumber=roomNum;
}

public int getRoomNumber()
{
    return roomNumber;
}

}

this.guestName[i]=guestName[i]; guestName is passed null in the constructor. — Subir Kumar Sao
– Subir Kumar Sao, Commented Apr 22, 2014 at 6:43

Hans · Accepted Answer · 2014-04-22 06:44:44Z

1

Why not get user input, and then make room for it? After user has entered the data (and you saved it to variables)

Room room1 = new Room(false, true, nameList, phoneInput, roomNumber);

answered Apr 22, 2014 at 6:44

Hans

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Comments

Rahul · Accepted Answer · 2014-04-22 06:42:59Z

0

That's because in your Room() constructor, you're doing this.

for (int i=0;i<4;i++)
    this.guestName[i]=guestName[i];

But you're passing null for the guestName as the parameter, which throws a NPE as your guestName array is null.

If you want to pass a null, remove the for loop from the constructor. If not, pass a blank String[] to the constructor.

Room room1 = new Room(false, false, new String[4], null, numberOfRooms);

Note that even when you do the above, each element in the String[] is still a null reference only and you need to explicitly initialize them in your program later.

answered Apr 22, 2014 at 6:42

Rahul

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Comments

TheWalkingCube · Accepted Answer · 2014-04-22 06:44:37Z

0

guestName is null in

 Room room1 = new Room(false, false, null, null, numberOfRooms);

but your constructor requires it not to be null

for (int i=0;i<4;i++)
    this.guestName[i]=guestName[i];

You should either add a test in your constructor :

if(guestName != null)

or pass a valid array when you call the constructor

answered Apr 22, 2014 at 6:44

TheWalkingCube

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Comments

Pramod S. Nikam · Accepted Answer · 2014-04-22 06:46:54Z

0

You are trying access guest name in constructor Which is null. Take care that , You Should not do any operation on on values those are passed/assigned/turned Null.

answered Apr 22, 2014 at 6:46

Pramod S. Nikam

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Comments

Michaël · Accepted Answer · 2014-12-18 10:30:09Z

0

In your for loop

for (int i=0;i<4;i++)
    this.guestName[i]=guestName[i];

The Argument guestName is null. Since you do not provide any value to it:

    Room room1 = new Room(false, false, null, null, numberOfRooms);

See the 3rd arugment.

edited Dec 18, 2014 at 10:30

Michaël

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answered Apr 22, 2014 at 6:45

Marcinek

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