Tree.java

/*
 * Copyright (c) 2003-2012 Fred Hutchinson Cancer Research Center
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.fhcrc.cpl.toolbox.datastructure;

import java.util.List;
import java.util.ArrayList;


/**
 * Represents a Tree of Objects of generic type T. The Tree is represented as
 * a single rootElement which points to a List<TreeNode<T>> of children. There is
 * no restriction on the number of children that a particular node may have.
 * This Tree provides a method to serialize the Tree into a List by doing a
 * pre-order traversal. It has several methods to allow easy updation of Nodes
 * in the Tree.
 * 
 * This class cribbed from the freely-available:
 * http://sujitpal.blogspot.com/2006/05/java-data-structure-generic-tree.html
 */
public class Tree<T> {
 
    private TreeNode<T> rootElement;
     
    /**
     * Default ctor.
     */
    public Tree() {
        super();
    }
 
    /**
     * Return the root Node of the tree.
     * @return the root element.
     */
    public TreeNode<T> getRootElement() {
        return this.rootElement;
    }
 
    /**
     * Set the root Element for the tree.
     * @param rootElement the root element to set.
     */
    public void setRootElement(TreeNode<T> rootElement) {
        this.rootElement = rootElement;
    }
     
    /**
     * Returns the Tree<T> as a List of Node<T> objects. The elements of the
     * List are generated from a pre-order traversal of the tree.
     * @return a List<Node<T>>.
     */
    public List<TreeNode<T>> toList() {
        List<TreeNode<T>> list = new ArrayList<TreeNode<T>>();
        walk(rootElement, list);
        return list;
    }
     
    /**
     * Returns a String representation of the Tree. The elements are generated
     * from a pre-order traversal of the Tree.
     * @return the String representation of the Tree.
     */
    public String toString() {
        return toList().toString();
    }
     
    /**
     * Walks the Tree in pre-order style. This is a recursive method, and is
     * called from the toList() method with the root element as the first
     * argument. It appends to the second argument, which is passed by reference     * as it recurses down the tree.
     * @param element the starting element.
     * @param list the output of the walk.
     */
    private void walk(TreeNode<T> element, List<TreeNode<T>> list) {
        list.add(element);
        for (TreeNode<T> data : element.getChildren()) {
            walk(data, list);
        }
    }
}