Node preX = x.getPrev();
Node nexX = x.getNext();
Node preY= y.getPrev();
Node nexY= y.getNext();

//edge case #1: x or y has nothing.
if(x==null || y == null) return;

//edge case #2: x == y, nothing to swap
if(x==y) return; //nothing to swap;

//edge case #3: edge case #3: x is right next to y

if (x.getNext() == y)
{
preX.setNext(y);
y.setPrev(preX);
nexY.setPrev(x);
x.setNext(nexY);
x.setPrev(y);
y.setNext(x);
}
else if(y.getNext() == x)
{
    preY.setNext(x);
    x.setPrev(preY);
    nexX.setPrev(y);
    y.setNext(nexX);
    y.setPrev(x);
    x.setNext(y);
else
{
//swap part
y.setPrev(preX);
y.setNext(nexX);
nexX.setPrev(y);
preX.setNext(y);

x.setPrev(preY);
x.setNext(nexY);
nexY.setPrev(x);
preY.setNext(x);
}