Java for loop to create n amount of object

Question

I need some help. I want to create a for loop that creates n number of objects of a class, and then adds them into an arraylist. Something like this:

//Player is a custom class 
ArrayList<Player> numberofPlayersArray;
numberofPlayersArray = new ArrayList<Player>();

//n is a variable for the number of Player class objects that I want to create
  for(int i = 0; i < n; i++)
  {

    //this is what I can come up with but I am missing something 

     Player p;
     p = new Player
     numberofPlayersArray.add(p);

    }

Any help would be appreciated

You are thinking correct. What's the problem? Is that the source code you're trying to compile? In that case, add () after new Player. Like this: Player p = new Player(); numberOfPlayers.add(p); (assuming your Player class has a default constructor. — Yngve Sneen Lindal
– Yngve Sneen Lindal, Commented Nov 29, 2009 at 16:26
problem is p must be null because I get a java.lang.NullPointerException when I call p.method(); — Sizemj
– Sizemj, Commented Nov 29, 2009 at 17:08

Gibbs · Accepted Answer · 2022-05-31 13:29:12Z

5

//Player is a custom class 
ArrayList<Player> numberofPlayersArray = new ArrayList<Player>(n);

//n is a variable for the number of Player class objects that I want to create
for(int i = 0; i < n; i++) {

     Player p = new Player();
     numberofPlayersArray.add(p);
}

Note that it's better to initialize the ArrayList with the size, if it is known (as in your case)

edited May 31, 2022 at 13:29

Gibbs

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answered Nov 29, 2009 at 16:26

Bozho

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4 Comments

Sizemj Over a year ago

OK now how would I call p.method(); ie: p.dosomething();

Bozho Over a year ago

what do you mean 'how would I call'? Just call it as you wrote.

Sizemj Over a year ago

problem is p must be null because I get a java.lang.NullPointerException when I call p.method();

Bozho Over a year ago

ask another question including the entire source code and point where the null pointer exception happens.

Asaph · Accepted Answer · 2009-11-29 16:31:04Z

5

Your code looks syntactically correct with one exception.

Change

p = new Player

to

p = new Player();

I'm assuming the variable n is declared and initialized and the Player class is defined with an argless constructor.

edited Nov 29, 2009 at 16:31

answered Nov 29, 2009 at 16:24

Asaph

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Comments

Andreas Dolk · Accepted Answer · 2009-11-29 16:25:56Z

0

I don't see a problem here, just do

p = new Player();

(but this might just have been a typo) and the playerlist will be populated with n different Player objects.

Note, that I'm just assuming, you want to use the default constructor for Player.

Naming hint: you shouldn't name a List '..Array', unless you want to confuse yourself ;) Just name it '..List'

answered Nov 29, 2009 at 16:25

Andreas Dolk

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Comments

Fortyrunner · Accepted Answer · 2009-11-29 17:33:48Z

0

Don't forget to code to the interface (rather than the concrete class).

List<Player> numberofPlayers = new ArrayList<Player>(n);

Forgetting to do this (or not knowing about it) is a common beginners mistake.

If you decide to switch to an alternative list implementation later on (LinkedList or maybe a Google Collection or an Apache Commons Collection list) you won't have to change every reference to the list - just the initial allocation.

answered Nov 29, 2009 at 17:33

Fortyrunner

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