在 testMain.java class 中非常插入（int 数据）函数调用之前将根设置为 null，如 btree.insert(1)；和 btree.insert(2)；

Question

below is the code for BinaryTree.java insertion . Every time i insert a new node , the root is null.What i want , after 1st insert , root should not be null and it should remember the 1st insert and then for 2nd insert, the condition if (root ==null) should be false.

import java.util.LinkedList;

public class BinaryTree {


    private  BTNode root;
    public int size;
    public BinaryTree(){
        this.root= null;
    }

 // public BTNode getRoot(){
     //   return this.root;
     //  }


    public void insert(int data){
     insert(data, root);
           //calling insert function that takes data and root to insert
    }

    private void  insert (int data, BTNode root){



        //case 1: no element in binary tree
        if (root == null){
              // if root is null create a new BTNode and make it root
            BTNode newN= new BTNode(data);
            newN.setLeft(null);
            newN.setRight(null);

            root =newN;
            //System.out.println(root.getData());
            size++;
            return;
            //return root.getData();    

        }
        //case2: tree not empty
            //create a queue and traverse each node left-right
        LinkedList<BTNode> q = new LinkedList<BTNode>();
            q.addFirst(root);


            while(!(q.isEmpty())){ //if queue not empty

                BTNode temp= (BTNode) q.removeFirst();

                //check left 
                if (temp.getLeft()==null){
                    //create a node and set left
                    BTNode newN= new BTNode(data);
                    newN.setLeft(null);
                    newN.setRight(null);
                    temp.setLeft(newN);
                    size++;
                    return;
                    //return root.getData();
                }
                else{

                    q.addLast(temp.getLeft());
                }


                //check right in case left is not null
                if (temp.getRight()==null){
                    //create a node and set right
                    BTNode newN= new BTNode(data);
                    newN.setLeft(null);
                    newN.setRight(null);
                    temp.setRight(newN);
                    size++;
                    return;
                    //return root.getData();

                }
                else{

                    q.addLast(temp.getRight());


                }



            }//while loop ends here


        return ;




    }// insert(data,root) function ends here

}//class ends here

below is code for BTNode.java

public class BTNode {


    int data;
    private BTNode left=null;

    private BTNode right=null;

    public BTNode(){

    }

    public BTNode(int data){
        this.data=data;


    }

    public int getData() {
        return data;
    }

    public void setData(int data) {
        this.data = data;
    }

    public BTNode getLeft() {
        return left;
    }

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

    public BTNode getRight() {
        return right;
    }

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



}

TestMain.java

public class TestMain {

    public static void main(String[] args){

        BinaryTree btree = new BinaryTree();
        btree.insert(1);

          //System.out.println(btree.getRoot().getData());
        btree.insert(2);

        btree.insert(3);

        btree.insert(4);
        btree.insert(5);
        btree.insert(6);

   }
}

Answer 1

TestMain.Java

public class TestMain {

public static void main(String[] args){

    BinaryTree btree = new BinaryTree();
    btree.insert(1);

    System.out.println(btree.getRoot().getData());
}

二叉树内部：

public BTNode getRoot(){
   return this.root;
}
private void  insert (int data, BTNode rootParameter){ // your problem is here

    //case 1: no element in binary tree
    if (root == null){
          // if root is null create a new BTNode and make it root
        BTNode newN= new BTNode(data);
        newN.setLeft(null);
        newN.setRight(null);

        root =newN;
        //System.out.println(root.getData());
        size++;
        return;
        //return root.getData();    

    }
    // other part of your code
}

问题是您正在将根分配给参数，但您应该将其分配给方法之外的根变量。你现在不会得到空引用。

在 testMain.java class 中非常插入（int 数据）函数调用之前将根设置为 null，如 btree.insert(1)；和 btree.insert(2)；

Root is set null before very insert(int data) function call in testMain.java class like btree.insert(1); and btree.insert(2);

java

recursion

binary-tree

data-structures