Question

I have implemented a program that stores sets within a Linkedlist. When I print out the linked lists, I get, for example, [1,2,3,4,5].

What I want is to change the square brackets to braces e.g. ‘{‘ & ‘}’

I can’t use string manipulations so I MUST override the toString method.

I am clueless on how to do this other than the fact I know i must create a subclass. It’s the method itself that baffles me.

public class outputSets
    {    
        @SuppressWarnings({ "unchecked", "rawtypes", "unused" })
        public static void main(String args[]) 
        {    
        LinkedList x0 = new LinkedList();
        LinkedList x1 = new LinkedList();
        LinkedList x2 = new LinkedList();
        LinkedList x3 = new LinkedList();
        LinkedList x4 = new LinkedList();
        LinkedList x5 = new LinkedList();
        LinkedList x6 = new LinkedList();

        x0.add(new Integer(8));

        for(int i=1; i<8; i++)
        {
            x1.add(new Integer(i));
        }

        x1.add((x0.getFirst()));

        x2.addAll(x1);
        x2.add(new Pair(1, x1));

        x3.add(new Pair(x2,x1));

        //x4.addAll(tree.union(x3, x2));

        //x5.add(tree.difference(x4, x1));

        //x6.add(tree.intersection(x4, x1));
        /*
        Iterator i0 = x0.listIterator();
        Iterator i1 = x0.listIterator();
        Iterator i2 = x0.listIterator();
        Iterator i3 = x0.listIterator();
        Iterator i4 = x0.listIterator();
        Iterator i5 = x0.listIterator();
        Iterator i6 = x0.listIterator();
        */

        System.out.print(x0.getFirst());
        System.out.println();
        SetArray(x1);
        System.out.println();
        SetArray(x2);

        System.out.println();
        System.out.println();
      }


    @SuppressWarnings("rawtypes")
    private static void SetArray(LinkedList x0)
    {
        for(int index=0; index < x0.size() ; index++)
        {
            if (index == 0)
            {
                System.out.print(x0.get(index));
            }
            else
            {
                System.out.print(", " +
                        "" + x0.get(index));
            }
        }

    }
}

Answer 1

The output is completely dependent on the implementation of AbstractCollection.toString() – which LinkedList (and most other collections except maps) inherits. This implementation looks like this (slightly simplified):

public String toString() {
    Iterator<E> it = iterator();
    if (! it.hasNext())
        return "[]";

    StringBuilder sb = new StringBuilder();
    sb.append('[');
    for (;;) {
        E e = it.next();
        sb.append(e);
        if (! it.hasNext())
            return sb.append(']').toString();
        sb.append(", ");
    }
}

Having this as a guideline it should be pretty straightforward for you to create your own implementation that does not include square brackets. You can either create your own collection that overrides toString() or have a separate utility method taking your LinkedList input as an argument (in that case obviously replace iterator() with input.iterator()).