find object by id from nested object list in java

Question

I have a java bean class :

class Node{

    int id, parentId;
    String value;
    List<Node> childs;

}

How could i find a parent node in this hierarchy and insert a child node in the child list of parent node. relationship between to node is defined as : if node1.id == node2.parentid then node2 will be in child list of node1.

This can be Nth level hierarchy.

Answer 1

In order to find a node in that hierarchy, you'll have to implement a method for traversing. I suggest using a recursive method and employ either a breadth-first or depth-first search pattern. Once you've located the correct Node, insert the child.

For instance:

public Node search(Node root, int searchId) {
    if (root.id == searchId) {
        return root;
    } else {
        for (Node child : root.childs) {
            Node node = search(child, searchId);
            if (node != null) {
                return node;
            }
        }
    }
    return null;
}

public void insert(Node node) {
    Node parent = search(root, node.parentId);
    if (node != null) {
        parent.childs.add(node);
    }
}

Answer 2

Try something like this

insertNode(Node nodeToInsert, Node anyNodeInHirarchy) {
        Node parent = getParentNodeById(anyNodeInHirarchy.parentId);
        if(parent.Id == nodeToInsert.parentId) {
            parent.childs.add(nodeToInsert);
        } else {
            insertNode(nodeToInsert, parent)
        }
    }
    return getParentNodeById(int nodeId) {
        // Find node by id and return
        return node;
    }

Answer 3

easily :

childNode.setParentId(parentNode.getId());
parentNode.getChilds().add(childNode);

Answer 4

Fast way of doing it is Guid should point the object easily so that you can point nth node easily.

Generate a Single Random GUID for eg : say 45892 Root node will point to that id. child will point in the pattern Parent_ID+"-"+Index_Number If consider three child will have 45892-0, 45892-1, 45892-2 And child of first node becomes - 45892-0-1, 45892-0-2

So you can travel directly using the id as faster and need not search, search time will be saved.

If you don't understand please comment. I will show in programming.

Note : ID length grows as depends on your level of usage.

If you have data already in the db or some persistent store.then you can prefer jgitter code. if not you can prefer this.

     class Node {
                public String id;
                public String parentId;
                public List<Node> childs;

            } 

            class Operation {
                public Node getChildNodeByID(Node root,String parentId) {
                    String[] keys = parentId.split("-");
                    Node parentNode = root;
                    int index = 0;
                    for(String key : keys ) {     
                        if(index == 0) {
                            if( !root.id.equals(key) ) {
                               throw new IllegalArgumentException("Root node does not match so parent node will not be found in this node");
                            }
                        }else {
                            int myIndex = Integer.parseInt(key);
                            if( parentNode.childs.getSize() > myIndex ) {
                                parentNode = parentNode.childs.get(myIndex);
                            }else {
                                throw new IllegalArgumentException("Parent Node does not exist");
                            }
                        }   
                        index++;
                    }
return parentNode;
                }

              public insert(Node node,Node root) {
                   Node parentNode =  getChildNodeByID(root,node.parentId);                  
                   node.id = node.parentId+"-"+parentNode.childs.getSize();
                   parentNode.childs.add(node);  
              }
            }