如何在Java中創建樹結構？

Question

我正在創建一個樹形結構，但問題是在輸入顯示時它不顯示任何東西。也許是因爲根目前仍然是空的，我不明白爲什麼。

public class Tree extends LLQueue { 

int data12; 
tree left; 
tree right; 


@Override 
public int getdata(){ 
    return data12; 
} 

@Override 
public void setdata(int data){ 
    this.data12 =data; 
} 
public tree getleft(){ 
    return left; 
} 
public void setleft(tree left){ 
    this.left=left; 
} 
public tree getright(){ 
    return right; 
} 
public void setright(tree right){ 
    this.right =right; 
} 

public static void main(String args[]) throws IOException, EmptyQueueException{ 
    BufferedReader br =new BufferedReader(new InputStreamReader(System.in)); 
    System.out.println("enter option "); 
    int n =Integer.parseInt(br.readLine()); 
    tree root =null; 
    do{ 
     System.out.println("\nQueue Operations"); 
     System.out.println("1. insert"); 
     System.out.println("2. display"); 

     int choice = Integer.parseInt(br.readLine()); 
     switch(choice){ 
      case 1: 

       System.out.println("insert here"); 
       int input =Integer.parseInt(br.readLine()); 
       insertintree(root,input); 
       break; 

      case 2: 
       System.out.println("result is"); 
       preorder(root); 

     } 
    }while(n!=0); 
} 
private static void insertintree(tree root, int input) throws EmptyQueueException { 
    LLQueue Q =new LLQueue(); 
    tree temp = null; 
    int temp1; 
    tree newnode =new tree(); 
    newnode.setdata(input); 
    newnode.setleft(null); 
    newnode.setright(null); 

if(newnode ==null){ 
    System.out.println("memory error"); 
    return; 
} 
if(root ==null){ 
    root =newnode; 
    return; 
} 
Q.enQueue(root.getdata()); 
while(!Q.isEmpty()){ 
     temp1=Q.deQueue(); 
     temp.setdata(temp1); 
     if(temp.getleft()!=null){ 
      tree temp2 =temp.getleft(); 

     Q.enQueue(temp2.getdata()); 
     } 
     else 
     { 
      temp.setleft(newnode); 
      Q.deQueue(); 
      return; 
     } 
      if(temp.getright()!=null){ 
      tree temp2 =temp.getright(); 

     Q.enQueue(temp2.getdata()); 
     } 
     else 
     { 
      temp.setright(newnode); 
      Q.deQueue(); 
      return; 
     } 
} 
Q.deQueue(); 

} 
private static void preorder(tree root) { 

    if(root!=null){ 

     System.out.println(root.getdata()); 
     preorder(root.getleft()); 
     preorder(root.getright()); 
    } 
} 
} 

Answer 1

你的問題是你需要返回所創建將其設置爲根的新節點。或者你也可以暴露的制定者根節點

使用此代碼對你的方法

private static Tree insertintree(tree root, int input) throws EmptyQueueException { 
    LLQueue Q =new LLQueue(); 
    tree temp = null; 
    int temp1; 
    tree newnode =new tree(); 
    newnode.setdata(input); 
    newnode.setleft(null); 
    newnode.setright(null); 
if(newnode ==null){ 
    System.out.println("memory error"); 
    return null; 
} 
    return newnode; 
} 

而且你在主代碼將變更爲

switch(choice){ 
     case 1: 

      System.out.println("insert here"); 
      int input =Integer.parseInt(br.readLine()); 
      Tree treeNode = insertintree(root,input); 
      if(treeNode!=null && root==null) {root = treeNode;} 
      break;