Java完全二叉树的创建与四种遍历方法分析

import java.util.ArrayDeque;import java.util.ArrayList;import java.util.List;import java.util.Queue;class Node {  public Node leftchild;  public Node rightchild;  public int data;  public Node(int data) {    this.data = data;  }}public class TestBinTree {    public Node initBinTree(int[] arr) {    if(arr.length == 1) {      return new Node(arr[0]);    }    List<Node> nodeList = new ArrayList<>();    for(int i = 0; i < arr.length; i++) {      nodeList.add(new Node(arr[i]));    }    int temp = 0;    while(temp <= (arr.length - 2) / 2) { //注意这里，数组的下标是从零开始的      if(2 * temp + 1 < arr.length)        nodeList.get(temp).leftchild = nodeList.get(2 * temp + 1);      if(2 * temp + 2 < arr.length)        nodeList.get(temp).rightchild = nodeList.get(2 * temp + 2);      temp++;    }    return nodeList.get(0);    }     public void trivalBinTree(Node root, Queue<Node> nodeQueue) {    nodeQueue.add(root);    Node temp = null;    while ((temp = nodeQueue.poll()) != null) {      System.out.print(temp.data + " ");      if (temp.leftchild != null) {        nodeQueue.add(temp.leftchild);      }      if (temp.rightchild != null) {        nodeQueue.add(temp.rightchild);      }    }  }       public void preTrival(Node root) {      if(root == null) {        return;      }      System.out.print(root.data + " ");      preTrival(root.leftchild);      preTrival(root.rightchild);    }        public void midTrival(Node root) {      if(root == null) {        return;      }      midTrival(root.leftchild);      System.out.print(root.data + " ");      midTrival(root.rightchild);    }        public void afterTrival(Node root) {      if(root == null) {        return;      }      afterTrival(root.leftchild);      afterTrival(root.rightchild);      System.out.print(root.data + " ");    }    public static void main(String[] args) {      TestBinTree btree = new TestBinTree();      int[] arr = new int[] {1,2,3,4,5,6,7};      Node root = btree.initBinTree(arr);      Queue<Node> nodeQueue = new ArrayDeque<>();      System.out.println("编程网测试结果：");      System.out.println("层序遍历：");      btree.trivalBinTree(root, nodeQueue);      System.out.println("\n先序遍历：");      btree.preTrival(root);      System.out.println("\n中序遍历：");      btree.midTrival(root);      System.out.println("\n后序遍历：");      btree.afterTrival(root);    }}