CODEWITHSUNDEEP
javalistlinked-list
Jessy
Jessy

Reputation: 15661

How to remove specific element on List

How to remove specific element on List?

...
java.util.List<Polygon> triangles = new LinkedList<Polygon>();
Point startDrag, endDrag, midPoint;
Polygon triangle;

....
int[] xs = { startDrag.x, endDrag.x, midPoint.x };
int[] ys = { startDrag.y, startDrag.y, midPoint.y };    

triangles.add( new Polygon(xs, ys,3));   
....

public void mouseClicked(MouseEvent e) {
...
   startDrag = new Point(e.getX(), e.getY());
   for (Polygon p:triangles){
    if (p.contains(startDrag)) //Polygon has a 'contains(Point)' method
           remove (p.contains(startDrag));
   }
....

Upvotes: 1

Views: 7289

Answers (3)

Nicholas Jordan
Nicholas Jordan

Reputation: 656

This is a nasty, I dug it - it's the system thread from the Mouse Clicked being identified as not the creator of the java.util.Thingamabob ( a new data structure to be released tomorrow )

Despite documentation, in alignment with common sense, what the thing does actually is see that the thread from MouseClicked is not the Thread that created

java.util.List<Polygon> triangles

using something on the order of Thread ID or such as naming of threads go and then throws from deep within the JVM an exception ( sets the exception flag on the C side ) then returns leaving you with no functioning exception.getMessage() .....

You can implement copy semantics and the original version will work, does some bit-twisting on your brain but it works.

Upvotes: 0

Gunslinger47
Gunslinger47

Reputation: 7061

To remove by object, such as removing a specific triangle from a triangle list, use List::remove(Object)

For the above purposes, you might want to use List::listIterator(), though. Something like:

ListIterator<Polygon> it = triangles.listIterator();
while (it.hasNext()) {
  if (it.next().contains(startDrag)) {
    it.remove();
    break;
  }
}

Upvotes: 3

akf
akf

Reputation: 39485

You will not be able to remove the object from the triangles list if you are currently iterating over it. If you try to do so, you will trigger a ConcurrentModificationException. Instead, what you should do is make a copy of the list and iterate over that, and when you get a hit, remove the item from the original:

public void mouseClicked(MouseEvent e) {
...
   Polygon[] triArray = triangles.toArray(new Polygon[triangles.size()]);
   startDrag = new Point(e.getX(), e.getY());
   for (Polygon p:triArray){
    if (p.contains(startDrag)) //Polygon has a 'contains(Point)' method
           triangles.remove (p);
   }
....

Upvotes: 2

Related Questions