NullPointerException when adding a new object to an array

Question

I am trying to add a Play name and length for a Theatre Seat Management Program. I want to be able to add new plays that will be on show at the theatre. Currently I have the following for class Play and its subclasses LocalPlay and ForeignPlay

public class Play {
public String name;
public double length;

public Play(String name, double length){
    this.name = name;
    this.length = length;
}


public void printPlayList(){
    System.out.print("name = " + this.name);
    System.out.print("length - " + this.length);
}   

}


class ForeignPlay extends Play{

public ForeignPlay(String name, double length){
    super(name, length);
}

}

class LocalPlay extends Play{

public LocalPlay(String name, double length){
    super(name, length);
}

}

For my Admin class (the class I wish to use the addPlay function within), I am trying to add new objects to the class by passing a String and double. This is my code:

public class Admin extends User{

private Play [] play;
private int size = 0;

public void addForeignPlay(String name, double length){
    this.play[size] = new ForeignPlay(name,length);
    this.size++;
}

public void addLocalPlay(String name, double length){
    this.play[size] = new LocalPlay(name,length);
    this.size++;
}

public void playDetails(){
    for(int i = 0; i < this.size; i++)
    this.play[i].printPlayList();
}

public static void main (String[] args){
    Admin testAdmin = new Admin();
    testAdmin.addLocalPlay("test", 125);
    testAdmin.playDetails();
}

}

When attempting to run this, I would expect to have an output of 'Test' and 125.0. However, I am receiving the error message:

Exception in thread "main" java.lang.NullPointerException at Admin.addLocalPlay(Admin.java:18) at Admin.main(Admin.java:33)

Thank you kindly for any help you can provide

You're not initializing `play` array anywhere, so it's null.. — Ori Lentz, Apr 10 '16 at 05:29
Possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — P.J.Meisch, Apr 10 '16 at 05:58

Rahman · Answer 1 · 2016-04-10T06:16:15.750

1

Replace private Play [] play; with private Play [] play = new Play[10]; Without initializing an array you cannot store any value in that array

edited Apr 10 '16 at 06:16

answered Apr 10 '16 at 05:30

Rahman

3,755
3
26
43

score 0 · Answer 2 · answered Apr 10 '16 at 05:34

Suggestion for your Admin class:

public class Admin extends User {

    private ArrayList<Play> playList = new ArrayList<>();

    public void addForeignPlay(String name, double length) {
        this.playList.add(new ForeignPlay(name, length));
    }

    public void addLocalPlay(String name, double length) {
        this.playList.add(new LocalPlay(name, length));
    }

    public void playDetails() {
        for (int i = 0; i < playList.size(); i++) {
            this.playList.get(i).printPlayList();
        }
    }

    public static void main(String[] args) {
        Admin testAdmin = new Admin();
        testAdmin.addLocalPlay("test", 125);
        testAdmin.playDetails();
    }
}

score 0 · Answer 3 · answered Apr 10 '16 at 05:34

0

In Java, arrays are not dynamic (the size is fixed and determined at his creation). If you want dynamic data structure, you should use an ArrayList for exemple.

answered Apr 10 '16 at 05:34

grebesche

511
1
3
14

score 0 · Answer 4 · answered Apr 10 '16 at 05:54

0

You should initialise the play variable like

private Play [] play = new Play[100]

or use constructor

public Admin(Play[] play, int size) {
    this.play = play;
    this.size = size;
}

answered Apr 10 '16 at 05:54

amith

399
1
2
11

NullPointerException when adding a new object to an array

4 Answers4