Way to access ArrayList from other method in same class without passing argument?

Question

I'm trying to have my method "add" access the contents of an ArrayList that was created in method "Friends", but Java isn't happy with what I'm doing (scope issues?). Is there a way to fix the problem without having to pass arguments?

public class Friends {
public Friends(float x, float y)
    {       
        ArrayList<MyObject> arrayList = new ArrayList<MyObject>(); 
        MyObject[] friendList = new MyObject[20];

    }

public void add()
    {       
        for (int i = 0; i < 20; i++) {
            //friendList[i]
        }
    }
}

note that Friends is meant to be a constructor (if I'm using that word right)

friendList should be a instance field instead of a local variable in the constructor — MadProgrammer
– MadProgrammer, Commented Nov 7, 2015 at 20:18

Andremoniy · Accepted Answer · 2015-11-07 20:17:56Z

4

Obviously for such cases you should use such called "object variables", or simply saying - fields of the class. You should make your variable arrayList part of the class as a field:

public class Friends {
List<MyObject> arrayList;
public Friends(float x, float y)
    {       
        arrayList = new ArrayList<MyObject>(); 
        MyObject[] friendList = new MyObject[20];

    }

public void add()
    {       
        for (int i = 0; i < 20; i++) {
            //arrayList.add(...).
        }
    }
}

answered Nov 7, 2015 at 20:17

Andremoniy

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Comments

Mohammed Aouf Zouag · Accepted Answer · 2015-11-07 20:18:09Z

1

Make your variables member variables of the Friends class:

public class Friends {
ArrayList<MyObject> arrayList;
MyObject[] friendList;
public Friends(float x, float y)
    {       
        arrayList = new ArrayList<MyObject>(); 
        friendList = new MyObject[20];

    }

public void add()
    {       
        for (int i = 0; i < 20; i++) {
            //friendList[i]
        }
    }
}

answered Nov 7, 2015 at 20:18

Mohammed Aouf Zouag

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Comments

Hendrik Simon · Accepted Answer · 2015-11-07 20:23:38Z

1

Your guess is correct. The problem here is scoping. You are creating a local variable arrayList in the constructor, which is only available in the constructor.

You should declare it as an instance variable like this:

public class Friends {

    ArrayList<MyObject> arrayList; = new ArrayList<MyObject>(); 
    MyObject[] friendList; = new MyObject[20];

    public Friends(float x, float y)
    {       
        this.arrayList = new ArrayList<MyObject>(); 
        this.friendList = new MyObject[20];
    }

public void add()
{       
    for (int i = 0; i < 20; i++) {
        //friendList[i]
    }
}

}

edited Nov 7, 2015 at 20:23

answered Nov 7, 2015 at 20:18

Hendrik Simon

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2 Comments

Giovanni Botta Over a year ago

"Global" is misleading. It's an instance or member variable.

Hendrik Simon Over a year ago

You're absolutely right I changed it to instance variable. Thanks.

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