Tree implementation in Java (root, parents and children)
Accepted answer throws a java.lang.StackOverflowError when calling the setParent or addChild methods.
Here's a slightly simpler implementation without those bugs:
public class MyTreeNode<T>{
private T data = null;
private List<MyTreeNode> children = new ArrayList<>();
private MyTreeNode parent = null;
public MyTreeNode(T data) {
this.data = data;
}
public void addChild(MyTreeNode child) {
child.setParent(this);
this.children.add(child);
}
public void addChild(T data) {
MyTreeNode<T> newChild = new MyTreeNode<>(data);
this.addChild(newChild);
}
public void addChildren(List<MyTreeNode> children) {
for(MyTreeNode t : children) {
t.setParent(this);
}
this.children.addAll(children);
}
public List<MyTreeNode> getChildren() {
return children;
}
public T getData() {
return data;
}
public void setData(T data) {
this.data = data;
}
private void setParent(MyTreeNode parent) {
this.parent = parent;
}
public MyTreeNode getParent() {
return parent;
}
}
Some examples:
MyTreeNode<String> root = new MyTreeNode<>("Root");
MyTreeNode<String> child1 = new MyTreeNode<>("Child1");
child1.addChild("Grandchild1");
child1.addChild("Grandchild2");
MyTreeNode<String> child2 = new MyTreeNode<>("Child2");
child2.addChild("Grandchild3");
root.addChild(child1);
root.addChild(child2);
root.addChild("Child3");
root.addChildren(Arrays.asList(
new MyTreeNode<>("Child4"),
new MyTreeNode<>("Child5"),
new MyTreeNode<>("Child6")
));
for(MyTreeNode node : root.getChildren()) {
System.out.println(node.getData());
}
Since @Jonathan's answer still consisted of some bugs, I made an improved version. I overwrote the toString() method for debugging purposes, be sure to change it accordingly to your data.
import java.util.ArrayList;
import java.util.List;
/**
* Provides an easy way to create a parent-->child tree while preserving their depth/history.
* Original Author: Jonathan, https://stackoverflow.com/a/22419453/14720622
*/
public class TreeNode<T> {
private final List<TreeNode<T>> children;
private TreeNode<T> parent;
private T data;
private int depth;
public TreeNode(T data) {
// a fresh node, without a parent reference
this.children = new ArrayList<>();
this.parent = null;
this.data = data;
this.depth = 0; // 0 is the base level (only the root should be on there)
}
public TreeNode(T data, TreeNode<T> parent) {
// new node with a given parent
this.children = new ArrayList<>();
this.data = data;
this.parent = parent;
this.depth = (parent.getDepth() + 1);
parent.addChild(this);
}
public int getDepth() {
return this.depth;
}
public void setDepth(int depth) {
this.depth = depth;
}
public List<TreeNode<T>> getChildren() {
return children;
}
public void setParent(TreeNode<T> parent) {
this.setDepth(parent.getDepth() + 1);
parent.addChild(this);
this.parent = parent;
}
public TreeNode<T> getParent() {
return this.parent;
}
public void addChild(T data) {
TreeNode<T> child = new TreeNode<>(data);
this.children.add(child);
}
public void addChild(TreeNode<T> child) {
this.children.add(child);
}
public T getData() {
return this.data;
}
public void setData(T data) {
this.data = data;
}
public boolean isRootNode() {
return (this.parent == null);
}
public boolean isLeafNode() {
return (this.children.size() == 0);
}
public void removeParent() {
this.parent = null;
}
@Override
public String toString() {
String out = "";
out += "Node: " + this.getData().toString() + " | Depth: " + this.depth + " | Parent: " + (this.getParent() == null ? "None" : this.parent.getData().toString()) + " | Children: " + (this.getChildren().size() == 0 ? "None" : "");
for(TreeNode<T> child : this.getChildren()) {
out += "\n\t" + child.getData().toString() + " | Parent: " + (child.getParent() == null ? "None" : child.getParent().getData());
}
return out;
}
}
And for the visualization:
import model.TreeNode;
/**
* Entrypoint
*/
public class Main {
public static void main(String[] args) {
TreeNode<String> rootNode = new TreeNode<>("Root");
TreeNode<String> firstNode = new TreeNode<>("Child 1 (under Root)", rootNode);
TreeNode<String> secondNode = new TreeNode<>("Child 2 (under Root)", rootNode);
TreeNode<String> thirdNode = new TreeNode<>("Child 3 (under Child 2)", secondNode);
TreeNode<String> fourthNode = new TreeNode<>("Child 4 (under Child 3)", thirdNode);
TreeNode<String> fifthNode = new TreeNode<>("Child 5 (under Root, but with a later call)");
fifthNode.setParent(rootNode);
System.out.println(rootNode.toString());
System.out.println(firstNode.toString());
System.out.println(secondNode.toString());
System.out.println(thirdNode.toString());
System.out.println(fourthNode.toString());
System.out.println(fifthNode.toString());
System.out.println("Is rootNode a root node? - " + rootNode.isRootNode());
System.out.println("Is firstNode a root node? - " + firstNode.isRootNode());
System.out.println("Is thirdNode a leaf node? - " + thirdNode.isLeafNode());
System.out.println("Is fifthNode a leaf node? - " + fifthNode.isLeafNode());
}
}
Example output:
Node: Root | Depth: 0 | Parent: None | Children:
Child 1 (under Root) | Parent: Root
Child 2 (under Root) | Parent: Root
Child 5 (under Root, but with a later call) | Parent: Root
Node: Child 1 (under Root) | Depth: 1 | Parent: Root | Children: None
Node: Child 2 (under Root) | Depth: 1 | Parent: Root | Children:
Child 3 (under Child 2) | Parent: Child 2 (under Root)
Node: Child 3 (under Child 2) | Depth: 2 | Parent: Child 2 (under Root) | Children:
Child 4 (under Child 3) | Parent: Child 3 (under Child 2)
Node: Child 4 (under Child 3) | Depth: 3 | Parent: Child 3 (under Child 2) | Children: None
Node: Child 5 (under Root, but with a later call) | Depth: 1 | Parent: Root | Children: None
Is rootNode a root node? - true
Is firstNode a root node? - false
Is thirdNode a leaf node? - false
Is fifthNode a leaf node? - true
Some additional informations: Do not use addChildren() and setParent() together. You'll end up having two references as setParent() already updates the children=>parent relationship.
Here is my implementation in java for your requirement. In the treeNode class i used generic array to store the tree data. we can also use arraylist or dynamic array to store the tree value.
public class TreeNode<T> {
private T value = null;
private TreeNode[] childrens = new TreeNode[100];
private int childCount = 0;
TreeNode(T value) {
this.value = value;
}
public TreeNode addChild(T value) {
TreeNode newChild = new TreeNode(value, this);
childrens[childCount++] = newChild;
return newChild;
}
static void traverse(TreeNode obj) {
if (obj != null) {
for (int i = 0; i < obj.childCount; i++) {
System.out.println(obj.childrens[i].value);
traverse(obj.childrens[i]);
}
}
return;
}
void printTree(TreeNode obj) {
System.out.println(obj.value);
traverse(obj);
}
}
And the client class for the above implementation.
public class Client {
public static void main(String[] args) {
TreeNode menu = new TreeNode("Menu");
TreeNode item = menu.addChild("Starter");
item = item.addChild("Veg");
item.addChild("Paneer Tikka");
item.addChild("Malai Paneer Tikka");
item = item.addChild("Non-veg");
item.addChild("Chicken Tikka");
item.addChild("Malai Chicken Tikka");
item = menu.addChild("Main Course");
item = item.addChild("Veg");
item.addChild("Mili Juli Sabzi");
item.addChild("Aloo Shimla Mirch");
item = item.addChild("Non-veg");
item.addChild("Chicken Do Pyaaza");
item.addChild("Chicken Chettinad");
item = menu.addChild("Desserts");
item = item.addChild("Cakes");
item.addChild("Black Forest");
item.addChild("Black Current");
item = item.addChild("Ice Creams");
item.addChild("chocolate");
item.addChild("Vanilla");
menu.printTree(menu);
}
}
OUTPUT
Menu
Starter
Veg
Paneer Tikka
Malai Paneer Tikka
Non-veg
Chicken Tikka
Malai Chicken Tikka
Main Course
Veg
Mili Juli Sabzi
Aloo Shimla Mirch
Non-veg
Chicken Do Pyaaza
Chicken Chettinad
Desserts
Cakes
Black Forest
Black Current
Ice Creams
chocolate
Vanilla
import java.util.ArrayList;
import java.util.List;
public class Node<T> {
private List<Node<T>> children = new ArrayList<Node<T>>();
private Node<T> parent = null;
private T data = null;
public Node(T data) {
this.data = data;
}
public Node(T data, Node<T> parent) {
this.data = data;
this.parent = parent;
}
public List<Node<T>> getChildren() {
return children;
}
public void setParent(Node<T> parent) {
parent.addChild(this);
this.parent = parent;
}
public void addChild(T data) {
Node<T> child = new Node<T>(data);
child.setParent(this);
this.children.add(child);
}
public void addChild(Node<T> child) {
child.setParent(this);
this.children.add(child);
}
public T getData() {
return this.data;
}
public void setData(T data) {
this.data = data;
}
public boolean isRoot() {
return (this.parent == null);
}
public boolean isLeaf() {
return this.children.size == 0;
}
public void removeParent() {
this.parent = null;
}
}
Example:
import java.util.List;
Node<String> parentNode = new Node<String>("Parent");
Node<String> childNode1 = new Node<String>("Child 1", parentNode);
Node<String> childNode2 = new Node<String>("Child 2");
childNode2.setParent(parentNode);
Node<String> grandchildNode = new Node<String>("Grandchild of parentNode. Child of childNode1", childNode1);
List<Node<String>> childrenNodes = parentNode.getChildren();