Question

I have tree where all leafs have index, when tree is rescursively lodaded form database, database will order tree by indexes. First it gets root nodes sorted by index and so on. Now I need to implement action how user can sort these indexes by pressing up/down arrow icons. When user presses down then index should take index that is under it’s own index and when up arrow is pressed it should do vice versa. I just don’t know what would be best way to implement this kind of functionality.

Answer 1

Since your question is a bit vague, this answer assumes you know what you are doing when it comes to the database stuff (I would reccommend hibernate for java if not) and the following code is meant to give you some ideas for implementing your solution.

//If I have understood your question, you want two nodes to swap position in the tree structure
public static swapNode(Node parent, Node child)
{
    Long superId = parent.getParentId();
    child.parentId(superId);
    parent.setParentId(child.getId());
    child.setId(parentId);
    //update children lists of parent and child
    //update parent ids of children lists

    //save changes to database
}

//create tree structure from database. Assumes nodes have been loaded from a database
//table where each row represents a node with a parent id column the root node which has parent id null)
//invoke this with all nodes and null for parentId argument
public static List<Node> createNodeTree(List<Node> allNodes, Long parentId)
{
    List<Node> treeList = new ArrayList<Node>();
    for(Node node : nodes)
    {
        if(parentIdMatches(node, parentId))
        {
            node.setChildren(createNodeTree(allNodes, node.getId()));
            treeList.add(node);
        }
    }
    return treeList;
}

private static boolean parentIdMatches(Node node, Long parentId)
{
    return (parentId != null && parentId.equals(node.getParentId())) 
        || (parentId == null && node.getParentId() == null);
}

//The objects loaded from the database should implement this interface
public interface Node
{
    void setParentId(Long id);
    Long getParentId();
    Long getId();
    List<Node> getChildren();
    void setChildren(List<Node> nodes);
}