How to delete from a list, while modifying the list [duplicate]

Question

I am trying to create a huffman tree, and am in the middle of attempting to merge two trees. I can not figure out how to remove a Tree in my program without getting the "concurrent Modification Exception" because I am iterating over a list and attempting to remove from the list at the same time.

BinaryTree<Character, Integer> t1 = null;
        BinaryTree<Character, Integer> t2 = null;
        BinaryTree<Character, Integer> tFinal = null;
        int treeSize = TREES.size();

        for (int i = 0; i < treeSize; i++) {

            for (BinaryTree<Character, Integer> t : TREES) {
                System.out.println("treeSize " + treeSize);
                System.out.println(t.getRoot().getElement()
                        + "  t.getRoot().getElement()");

                // here I edited the merge function in Binary Tree to set
                // the new root
                // to have null value for value, and itemTwo for weight
                System.out.println(t.getRoot().getValue() + " weight of tree \n");
                t1 = t;
                TREES.remove(t);

            }
            for (BinaryTree<Character, Integer> t : TREES){
                t2 = t;
                System.out.println(t);
            }
            int weight = t1.getRoot().getElement() + t2.getRoot().getElement();
            tFinal.merge(null, weight, t1, t2);
        }

Answer 1

Java prevents you from modifying collections in a loop. You will need to use an iterator.