Tree implementation in Java (root, parents and children)

Question

I need to create a tree structure similar as the attached image in Java. I've found some questions related to this one but I haven't found a convincing and well explained response. The application business consists in food super categories (main courses, desserts and other). Each of these categories can have parent items or children items and so on.

Answer 1

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()); } 

Answer 2

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();