import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;

/**
 * 二叉树深度优先遍历和广度优先遍历
 *     A
 *    / \
 *   B   C
 *  / \  /\
 * D  E F G
 *
 * @author <a href='mailto:zhaotengfei9@gmail.com'>Tengfei Zhao</a>
 */

public class DFS_BFS {
    @org.junit.Test
    public void main() throws Exception {
        TreeNode treeNode = new TreeNode("A");
        treeNode.left = new TreeNode("B", new TreeNode("D"), new TreeNode("E"));
        treeNode.right = new TreeNode("C", new TreeNode("F"), new TreeNode("G"));
        System.out.println("-----DFS------");
        DFS(treeNode);
        System.out.println("-----BFS------");
        BFS(treeNode);
    }

    /**
     * Depth First Search
     *
     * @param root
     */
    public void DFS(TreeNode root) {
        Stack<TreeNode> stack = new Stack<>();
        stack.add(root);
        while (!stack.isEmpty()) {
            // 移除最后一个
            TreeNode tempNode = stack.pop();
            System.out.println(tempNode.element);
            // 后进先出
            if (tempNode.right != null)
                stack.add(tempNode.right);
            if (tempNode.left != null)
                stack.add(tempNode.left);

        }
    }

    /**
     * Breadth First Search
     *
     * @param root
     */
    public void BFS(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        // 先进先出
        while (!queue.isEmpty()) {
            TreeNode tempTreeNode = queue.remove();
            System.out.println(tempTreeNode.element);
            if (tempTreeNode.left != null)
                queue.add(tempTreeNode.left);
            if (tempTreeNode.right != null)
                queue.add(tempTreeNode.right);
        }
    }

    class TreeNode {
        String element;
        TreeNode left;
        TreeNode right;

        TreeNode(String element) {
            this.element = element;
        }

        TreeNode(String element, TreeNode left, TreeNode right) {
            this.element = element;
            this.left = left;
            this.right = right;
        }
    }

}


打印结果：
-----DFS------
A
B
D
E
C
F
G
-----BFS------
A
B
C
D
E
F
G