一，定义一个节点类：

package test;

public class Node {
	private int data;
	private Node left;
	private Node right;
	public Node(int data) {
		this.data = data;
	}
	public int getData() {
		return data;
	}
	public void setData(int data) {
		this.data = data;
	}
	public Node getLeft() {
		return left;
	}
	public void setLeft(Node left) {
		this.left = left;
	}
	public Node getRight() {
		return right;
	}
	public void setRight(Node right) {
		this.right = right;
	}
	
}

二，定义一个算法实现类：

package test;

public class FindTree {

	private void visit(int data) {
		System.out.print(data+"--");
	}
	
	public void preOrder(Node root) {
		if(root == null) {
			return;
		}
		visit(root.getData());
		preOrder(root.getLeft());
		preOrder(root.getRight());
	}
	
	public void inOrder(Node root) {
		if(root == null) {
			return;
		}
		inOrder(root.getLeft());
		visit(root.getData());
		inOrder(root.getRight());
	}
	
	public void afterOrder(Node root) {
		if(root == null) {
			return;
		}
		afterOrder(root.getLeft());
		afterOrder(root.getRight());
		visit(root.getData());
	}
	
}

三，构建一个二叉树

package test;


public class TestTree {

	public static void main(String[] args) {
		FindTree ft = new FindTree();
		int[] array = {12,76,35,22,16,48,90,46,9,40};
		int j = 0;
		Node root = new Node(array[j]);
		for(int i = 1; i< array.length; i++) {
			insert(root, array[i]);
		}
		System.out.println("preorder----------------------------------");
		ft.preOrder(root);
		System.out.println("
inorder----------------------------------");
		ft.inOrder(root);
		System.out.println("
afterorder----------------------------------");
		ft.afterOrder(root);
		
	}

	private static void insert(Node root, int data) {
	      //二叉树中左边的孩子节点小于父节点，右边的孩子节点大于父节点
		if(root.getData() < data) {
			if(root.getRight() == null) {
				root.setRight(new Node(data));
			} else {
				insert(root.getRight(), data);
			}
		} else {
			if(root.getLeft() == null) {
				root.setLeft(new Node(data));
			} else {
				insert(root.getLeft(), data);
			}
		}
	} 
}

四，打印结果：

preorder----------------------------------

12--9--76--35--22--16--48--46--40--90--

inorder----------------------------------

9--12--16--22--35--40--46--48--76--90--

afterorder----------------------------------

9--16--22--40--46--48--35--90--76--12--