Adding new objects to an ArrayList in constructor

Question

I am trying to add newly created objects to an ArrayList in the constructor of a class. The new objects are being created in another class in the main method.

Main method:

public static void main(String[] args) {
    // TODO code application logic here
    Player p1 = new Player("Peter");
}

My Player class:

public class Player {

protected static int age;
protected static String name;
protected static ArrayList players = new ArrayList();

Player(String aName) {
    
    name = aName;
    age = 15;
    players.add(new Player()); // i know this doesn't work but trying along these lines
    
   }
}

You could try players.add(this) which refers to your current instance, but I my suggestion would be to revise your structure because I think it should not be the Player's duty to remember which players have been created so far. This functionality should be delegated to a dedicated entity — Morfic
– Morfic, Commented Oct 18, 2013 at 18:46
There could be legitamate reasons to keep a list of all players inside Player. I'm not saying I would do it this way, but you can make a perfectly workable program like this — Richard Tingle
– Richard Tingle, Commented Oct 18, 2013 at 18:47
I agree, there is always the possibility. I can't know what his exact thoughts are, but following his example and the usage of the static variables, I reached the above conclusion — Morfic
– Morfic, Commented Oct 18, 2013 at 19:00
It almost looks like a implementation of a linked list that uses ArrayList instead of Player previous;Player next I would bet that there will be a method next & previous. Otherwise I agree with @Grove that it should be delegated elsewhere — user2033671
– user2033671, Commented Oct 18, 2013 at 19:02

shikjohari · Accepted Answer · 2013-10-18 19:12:17Z

6

You have to edit the line

players.add(new Player());

to

players.add(this);

Also, there is no need to make the age and name static

I suggest you should have the following code instead

import java.util.ArrayList;

public class Player {

protected int age;    //static is removed
protected String name;  // static is removed
protected static ArrayList<Player> players = new ArrayList<Player>();  //this is not a best practice to have a list of player inside player.

Player(String aName) {

    name = aName;
    age = 15;
    players.add(this); // i know this doesn't work but trying along these lines

   }


public static void main(String[] args) {
    // TODO code application logic here
    Player p1 = new Player("Peter");
}


}

edited Oct 18, 2013 at 19:12

answered Oct 18, 2013 at 18:51

shikjohari

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2 Comments

Richard Tingle Over a year ago

Just adding a default constructor would lead to creation of a player having a different new player added to the arraylist, the OP is using new Player() to explain the concept of "this"

Chris Over a year ago

I managed to do it in the end and it was exactly along these lines. Thanks.

SLaks · Accepted Answer · 2013-10-18 18:44:07Z

2

It sounds like you're actually asking how to refer to the instance you're constructing.
That's what the this keyword does.

answered Oct 18, 2013 at 18:44

SLaks

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4 Comments

DarthVader Over a year ago

no. he is failing cause new Player() wont work, due to no default constructor.

SLaks Over a year ago

@DarthVader: Yes, but that doesn't make sense anyway.

Richard Tingle Over a year ago

@DarthVader I think the OP is using new Player() to express the concept of "this"

DarthVader Over a year ago

I think there is a design and understanding the concepts problem there. such as static props, and Player has players didnt make much sense to me

Haruki · Accepted Answer · 2017-11-08 07:40:59Z

This post is old, but for someone with similiar needs I suggest doing it like this:

Main class:

public static void main(String[] args) {
    //TODO code application logic here
    java.util.List<Player> players = new java.util.ArrayList<>(); //list to hold all players
    Player p1 = new Player("Peter"); //test player
    players.add(p1); //adding test player to the list
    players.add(new Player("Peter")); //also possible in this case to add test player without creating variable for it.
}

Player class:

public class Player {

    private final int age = 15; //if you always going to use 15 as a age like in your case it could be final. if not then pass it to constructor and initialize the same way as the name.
    private String name;

    Player(String name) { //variable name can be the same as one in class, just add this prefix to indicated you are talking about the one which is global class variable.
        this.name = name;
    }

}

Generally you should avoid using static keyword on variables which supposed to be different in each instance of that class. Avoid having object of itself inside.

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