Why are all of the nodes that I add to different lists ends up in one list?

Issue

I have two classes, RectNode and RectList. The assignment is to create a list of rectangles (with another class called RectangleA). When I use the tester it seems like all of the nodes are added to the all of lists, even tho I create different lists. For example, the tester creates two lists: rL1 and rL2. Then it adds one rectangle to the 1st list, and one to the 2nd. The problem is that when I run the tester and prints both lists with a toString() method I created, it shows that both rectangles are in both of the lists. Can anyone help me find the problem? When running test:

rL1: The list has 2 rectangles.

1. Width=5 Height=7 PointSW=(0,0)
2. Width=3 Height=8 PointSW=(0,0)

rL2: The list has 2 rectangles.

1. Width=5 Height=7 PointSW=(0,0)
2. Width=3 Height=8 PointSW=(0,0)

classes:

public class RectList
{
    private static RectNode _head;
    public RectList(){
        _head = null;
    }
    public static void addRect(RectangleA r){
        if(empty()){
            _head = new RectNode(r);
        }else{
            boolean isThereRectangle = false;
            RectNode ptr = _head;
            while(ptr.getNext() != null){
                if(ptr.getRect().equals(r)){
                    isThereRectangle = true;
                }
                ptr = ptr.getNext();
            }
            if(ptr.getRect().equals(r)){
                isThereRectangle = true;
            }
            if(isThereRectangle == false){
                ptr.setNext(new RectNode(r));
            }
        }
    }
    public String toString(){
        String list = "";
        int counter = 0;
        if(!empty()){
            RectNode ptr = _head;
            while(ptr != null){
                counter++;
                list += (counter + ". " + ptr.getRect().toString() + "\r\n");
                ptr = ptr.getNext();
            }
        }
        return ("The list has " + counter + " rectangles." + "\r\n" + list);
        
    }
}
public class RectNode
{
    private RectangleA _rect;
    private RectNode _next;
    public RectNode(RectangleA r){
        _rect = r;
        _next = null;
    }
    public RectNode(RectangleA r, RectNode n) {
        _rect = r;
        _next = n;
    }
    public RectNode(RectNode r){
        _rect = r._rect;
        _next = r._next;
    }
    public RectangleA getRect(){
        return new RectangleA(_rect);
    }
    public RectNode getNext(){
        return _next;
    }
    public void setRect(RectangleA r){
        _rect = new RectangleA(r);
    }
    public void setNext(RectNode next){
        _next = next;
    }
}

public class test
{
    public static void main(String[] args) {
        RectList rL1 = new RectList();
        RectList rL2 = new RectList();
        RectangleA r1 = new RectangleA(5, 7);
        RectangleA r2 = new RectangleA(3, 8);
        rL1.addRect(r1);
        rL2.addRect(r2);
        System.out.println("rL1: " + rL1.toString() +"\nrL2: " + rL2.toString());
    }
}

Solution

your _head variable is a static property of the RectList class . static members have the same value in all occurrences of the class. so when you do rL1.addRect(r1); rL2 also get r1 as it's head. then you do rL2.addrect(r2) and it adds r2 to the reference of the head, which is the same head of both objects (because the head is the static variable).

you can just remove the static keyword and it should do the trick.

Answered By - Daniel