Generic tree with breadth-first search.

PCTree.java

import static java.lang.System.*;
import java.util.ArrayList;


public class PCBTree {

	public static void main(String[] args) {        


		/** 
		* BUILD THAT TREE!
		*          O
		*         /\
		*       O   O
		*      /\
		*     O  O
		**/
		

		// Instantiate the root
		Node<String> root = new Node<>("I am root", null, null);

		// Instantiate all the children
		Node<String> childOne = new Node<String>("I am child one", root, null);
		Node<String> childTwo = new Node<String>("I am child two", root, null);

		Node<String> grandChildOne = new Node<String>("I am grandchild one", childOne, null);
		Node<String> grandChildTwo = new Node<String>("I am grandchild two", childOne, null);

		
		// You are the father!
		// (Adds corresponding children to their parents.)
		root.addChildren(childOne, childTwo);
		childOne.addChildren(grandChildOne, grandChildTwo);

		// Breadth first search
		root.breadthFirst();
	}
}



class Node<Element> {

	public Element contents;
	public Node<Element> parent;
	public ArrayList<Node<Element>> children;
	

	// Basic contructor
	public Node(Element contents, Node<Element> parent, ArrayList<Node<Element>> children) {
		this.contents = contents;
		this.parent = parent;

		// Checks to see if there are any children
		// If not, give them a home
		if (children == null) {
			this.children = new ArrayList<Node<Element>>();
		} else {
			this.children = children;
		}
		
	}

	// Add many children by a variadic parameter
	public void addChildren(Node<Element>... newChildren) {
		for (Node<Element> child : newChildren) {
			this.children.add(child);
		}
	}


	// Breadth-first Traversal
	public void breadthFirst() {
		ArrayList<Node<Element>> queue = new ArrayList<>(); // Java 7 trick

		// Treat the called node as root -- add to the queue
		queue.add(this);

		while (queue.size() != 0) {

			// Remove the node
			Node<Element> currentNode = queue.remove(0);

			// "Visit" It (in our case, print its contents)
			System.out.println(currentNode.contents);

			// Adds its children to the queue (to visit later)
			for (Node<Element> child : currentNode.children) {
				queue.add(child);
			}

		}

	}

}