Question

I have an home work,I used an array and element of array is linked list because the element in a row is not fixed need delete or add some time depend on problem condition , I was tried these codes below, but I have a problem when adding new element to a fixed row for example p[0] the value will be added for all, how I can solve this problem please help.

public class schedule
{
   public class link
   {
     public LinkedList <Integer>list = new LinkedList<Integer>() ;
     public link(LinkedList<Integer> value)
    {
        list = value;
    }
    public link(int value)
    {
        list.add(Integer.valueOf(value)) ;
    }

}


private link p[] = new link[10];
public schedule()
{
    LinkedList<Integer> l = new LinkedList<Integer>();
    l.add(Integer.valueOf(2));
    l.add(Integer.valueOf(0));
    l.add(Integer.valueOf(3));
    for(int j=0;j<p.length;j++)
        p[j] = new link(l);



    p[0].list.add(9); // here I  have problem

    for(int j=0;j<p.length;j++)
    {
        System.out.print("p["+j+"]:");
        for(int i=0;i<p[j].list.size();i++)
            System.out.print(p[j].list.get(i).intValue());
        System.out.println();
    }

}
public static void main(String []arg)
{
    new schedule();
}


the output is like this : the value 9 added to all but I want to be added just for first element
p[0]:2039
p[1]:2039
p[2]:2039
p[3]:2039
p[4]:2039
p[5]:2039
p[6]:2039
p[7]:2039
p[8]:2039
p[9]:2039

Answer 1

The problem is that you’re initializing every link instance with the same LinkedList<Integer>:

LinkedList<Integer> l = new LinkedList<Integer>();
l.add(Integer.valueOf(2));
l.add(Integer.valueOf(0));
l.add(Integer.valueOf(3));
for(int j=0;j<p.length;j++)
//it will be the same LinkedList<Integer> l per all the instances in the array
    p[j] = new link(l);

Take note that when you do this, every link instance will have the list attribute referencing the same LinkedList<Integer> l variable. So, if you modify it in one place, everyone will be updated (because it’s the same reference).

There are many ways to solve this:

• Create a new LinkedList on every iteration of your for loop.
• Create the new link instance using another constructor.
• Fill your link[] p array one by one…