java实现二叉树

首先创建一个类Node，定义二叉树Node.java

public class Node { //节点的定义
private int data;
private Node leftNode;
private Node rightNode;
public Node(int data, Node leftNode, Node rightNode){
this.data = data;
this.leftNode = leftNode;
this.rightNode = rightNode;
}

public int getData() { //获取数据值
return data;
}
public void setData(int data) { //设置数据值
this.data = data;
}
public Node getLeftNode() {      //获取左节点
return leftNode;
}
public void setLeftNode(Node leftNode) {    //设置左节点
this.leftNode = leftNode;
}
public Node getRightNode() {       //获取右节点
return rightNode;
}
public void setRightNode(Node rightNode) {     //设置右节点
this.rightNode = rightNode;
}
}

首先初始化二叉树，然后对二叉树进行遍历，包括前序遍历、中序遍历、后序遍历

public class BinaryTree {
public Node init() {//注意必须逆序建立，先建立子节点，再逆序往上建立，因为非叶子结点会使用到下面的节点，而初始化是按顺序初始化的，不逆序建立会报错
Node J = new Node(8, null, null);
Node H = new Node(4, null, null);
Node G = new Node(2, null, null);
Node F = new Node(7, null, J);
Node E = new Node(5, H, null);
Node D = new Node(1, null, G);
Node C = new Node(9, F, null);
Node B = new Node(3, D, E);
Node A = new Node(6, B, C);
return A; //返回根节点
}

public void printNode(Node node){
System.out.print(node.getData());
}
public void theFirstTraversal(Node root) { //先序遍历
printNode(root);
if (root.getLeftNode() != null) { //使用递归进行遍历左孩子
theFirstTraversal(root.getLeftNode());
}
if (root.getRightNode() != null) { //递归遍历右孩子
theFirstTraversal(root.getRightNode());
}
}
public void theInOrderTraversal(Node root) { //中序遍历
if (root.getLeftNode() != null) {
theInOrderTraversal(root.getLeftNode());
}
printNode(root);
if (root.getRightNode() != null) {
theInOrderTraversal(root.getRightNode());
}
}


public void thePostOrderTraversal(Node root) { //后序遍历
if (root.getLeftNode() != null) {
thePostOrderTraversal(root.getLeftNode());
}
if(root.getRightNode() != null) {
thePostOrderTraversal(root.getRightNode());
}
printNode(root);
}
public static void main(String[] args) {
BinaryTree tree = new BinaryTree();
Node root = tree.init();
System.out.println("先序遍历");
tree.theFirstTraversal(root);
System.out.println("");
System.out.println("中序遍历");
tree.theInOrderTraversal(root);
System.out.println("");
System.out.println("后序遍历");
tree.thePostOrderTraversal(root);
System.out.println("");
}
}

输出结果控制台输出为：