java遍历二叉树

public class TreeNode {
	private TreeNode left, right;

	private Object item;

	public TreeNode(Object item) {
		this(null, null, item);
	}

	public TreeNode(TreeNode left, TreeNode right, Object item) {
		this.left = left;
		this.right = right;
		this.item = item;
	}

	public TreeNode getLeft() {
		return left;
	}

	public void setLeft(TreeNode left) {
		this.left = left;
	}

	public TreeNode getRight() {
		return right;
	}

	public void setRight(TreeNode right) {
		this.right = right;
	}

	public Object getItem() {
		return item;
	}

	public void setItem(Object item) {
		this.item = item;
	}

}

public class ReadNode {

	public static void main(String[] args) {
		before(getTree());
		System.out.println();
		after(getTree());
		System.out.println();
		middle(getTree());
	}
<span style="white-space:pre">	</span>//构造一颗二叉树
	public static TreeNode getTree() {
		TreeNode g = new TreeNode('G');
		TreeNode d = new TreeNode(g, null, 'D');
		TreeNode e = new TreeNode('E');
		TreeNode b = new TreeNode(d, e, 'B');
		TreeNode h = new TreeNode('H');
		TreeNode f = new TreeNode(null, h, 'F');
		TreeNode c = new TreeNode(f, null, 'C');
		TreeNode a = new TreeNode(b, c, 'A');
		return a;
	}

	//前序遍历
	public static void before(TreeNode treeNode) {
		if(treeNode != null){
			visitNode(treeNode);
			before(treeNode.getLeft());
			before(treeNode.getRight());
		}
	}

	//后序遍历
	public static void after(TreeNode treeNode) {
		if(treeNode != null){
			after(treeNode.getLeft());
			visitNode(treeNode);
			after(treeNode.getRight());
		}
	}

	//中序遍历
	public static void middle(TreeNode treeNode) {
		if(treeNode != null){
			middle(treeNode.getLeft());
			middle(treeNode.getRight());
			visitNode(treeNode);
		}
	}

	public static void visitNode(TreeNode treeNode) {
		System.out.print(treeNode.getItem().toString());
	}

}