Java: How to have an ArrayList as instance variable of an object?

Question

I'm working on a class project to build a little Connect4 game in Java. My current thinking is to have a class of Columns that have as instance variable a few integers (index, max. length, isFull?) and one ArrayList to receive both the integers above and the plays of each players (e.g., 1's and 0's standing for X's and O's). This is probably going to be split between 2 classes but the question remains the same.

My current attempt looks like this:

import java.util.ArrayList;
public class Conn4Col {
    public int hMax; 
    public int index;
    public final int initialSize = 0;
    public final int fullCol = 0;
    public ArrayList<Integer>;
    (...)}

Unfortunately, this doesn't compile. The compiler says an <identifier> is missing where my ArrayList declaration stands.

We're just starting objects and we haven't really looked into other instance variables than the basic types.

Can someone tell me where my error is and how to correct it?

Gregory Pakosz · Accepted Answer · 2010-03-25 15:22:53Z

13

You forgot to give your member a name.

import java.util.ArrayList;
public class Conn4Col {
    public int hMax; 
    public int index;
    public final int initialSize = 0;
    public final int fullCol = 0;
    public ArrayList<Integer> list;
    (...)}

answered Mar 25, 2010 at 15:22

Gregory Pakosz

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1 Comment

JDelage Over a year ago

Thank you, this was effectively the problem.

pitpod · Accepted Answer · 2010-03-25 15:26:47Z

2

One more addition: better use java.util.List and only use the specific ArrayList during the creation of the object:

public List<Integer> list;
...
list = new ArrayList<Integer>();

That way you can change the actual implementation without having to change the member declaration.

answered Mar 25, 2010 at 15:26

pitpod

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Comments

Bob · Accepted Answer · 2019-11-28 03:43:49Z

2

public ArrayList<Integer> list;

But, do not declare ArrayList public:

private ArrayList<Integer> list = new ArrayList<Integer> ();

public List<Integer> getList ()
{
    return Collections.unmodifiableList(list);
}

edited Nov 28, 2019 at 3:43

Bob

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answered Mar 25, 2010 at 15:22

Alexander Pogrebnyak

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2 Comments

Sean Owen Over a year ago

This is good practice, but doesn't answer the question does it? He was missing a name for the variable.

BalusC Over a year ago

This is by the way not the root cause. See Gregory's answer for the real answer. You're simply forgotten the identifier, like as you have done for hMax, index, etc..etc..

Robby Pond · Accepted Answer · 2010-03-25 15:25:11Z

1

private List<Integer> list = new ArrayList<Integer>();

answered Mar 25, 2010 at 15:25

Robby Pond

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Comments

Anushil Kumar · Accepted Answer · 2020-09-07 08:51:22Z

0

You forgot to give the variable a name. Correct Syntax:

public ArrayList<Integer> listName;

answered Sep 7, 2020 at 8:51

Anushil Kumar

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