java - 无法解决java.lang.NullPointerException

Question

无论我尝试对框架类中的行 bTree.binaryTree[i].Data=in.nextLine(); 做什么，都会导致

Enter the Number of Nodes in the Binary Tree :5 Exception in thread "main" java.lang.NullPointerException Details for node#0 at binaryTree.framework.intialize(framework.java:19) Enter Data : at binaryTree.main.main(main.java:9) Process finished with exit code 1

Github要点:https://gist.github.com/D-codex/0051d59abb91fafc73fbec0fa7dad356

已编辑:https://gist.github.com/D-codex/009a5afa391c760b7ecc88f8109662c0(按照 GhostCat 的建议后)

我已尽力初始化几乎所有内容，以避免在任何地方出现“null”，但此异常不断弹出

节点类

package binaryTree;
import java.util.*;

public class node {
boolean hasLeft,hasRight;
boolean isRootPrimary,isRoot;
String Data;
String nodeID,leftNodeID,rightNodeID,parentID;
int childrenNodeCount;
node(){
    hasLeft=false;
    hasRight=false;
    Data="";
    childrenNodeCount=0;
}
void check(){
    if(hasLeft||hasRight)
        isRoot=true;
}
String fetchRoot(){
    return parentID;
}
String fetchID(){
    return nodeID;
}
String fetchSiblingID(){
    return "("+String.valueOf(leftNodeID)+" "+String.valueOf(rightNodeID)+")";
}
}

树类

package binaryTree;
import java.util.*;


public class Tree extends node{
node binaryTree[];
int count;int rootID,height,depth;
String siblingPairs,leaves;
Tree(int count){
    binaryTree=new node[count];
    this.count=count;
    rootID=0;
    height=0;depth=0;
}
void finalise(){
    for(int i=0;i<count;i++){
        if(binaryTree[i].childrenNodeCount==0)
            leaves=String.valueOf(binaryTree[i].fetchID());
        if(binaryTree[i].childrenNodeCount==2){
            siblingPairs=binaryTree[i].fetchSiblingID();
        }
    }
    StringTokenizer st=new StringTokenizer(leaves);
    while(st.hasMoreElements()){
        int counter=0;
        int leafID=Integer.valueOf(st.nextToken());
        node temp=binaryTree[leafID];
        while(temp.isRootPrimary){
            temp=binaryTree[Integer.valueOf(temp.fetchRoot())];
            counter=counter+1;
        }
        if(counter>height) {
            height = counter;
            depth=height-1;
        }
    }
}
}

框架类

package binaryTree;
import java.util.*;


public class framework {
public Tree intialize(){
    System.out.print("Enter the Number of Nodes in the Binary Tree    :");
    Scanner in=new Scanner(System.in);
    int count=in.nextInt();
    Tree bTree=new Tree(count);
    int ID=0;int i=0;
    while(i<count){
        System.out.println("Details for node#"+i);
        System.out.print("Enter Data  :");
        bTree.binaryTree[i].Data=in.nextLine();
        bTree.binaryTree[i].nodeID=String.valueOf(ID);
        if(i!=0){
            boolean flag = true;
            while (flag) {
                String parentID="";
                System.out.print("Enter the node's Parent:");
                parentID = in.nextLine();
                if     (bTree.binaryTree[Integer.valueOf(parentID)].childrenNodeCount >= 2) {
                    System.out.println("Parent Node is Full");
                }
                else {
                    bTree.binaryTree[i].parentID = in.nextLine();
                    bTree.binaryTree[Integer.valueOf(parentID)].childrenNodeCount=bTree.binaryTree[Integer.valueOf(parentID)].childrenNodeCount+1;
                    flag=false;
                }
            }
            System.out.print("Is the node Parent's Left?");
            String temp=in.next();
            if(temp.equalsIgnoreCase("yes")||temp=="1"||temp.equalsIgnoreCase("y")){
                bTree.binaryTree[Integer.valueOf(bTree.binaryTree[i].parentID)].hasLeft=true;
                bTree.binaryTree[Integer.valueOf(bTree.binaryTree[i].parentID)].leftNodeID=bTree.binaryTree[i].nodeID;
            }
            else {
                bTree.binaryTree[Integer.valueOf(bTree.binaryTree[i].parentID)].hasRight = true;
                bTree.binaryTree[Integer.valueOf(bTree.binaryTree[i].parentID)].rightNodeID=bTree.binaryTree[i].nodeID;
            }
        }
        else
            bTree.binaryTree[i].isRootPrimary=true;
        bTree.binaryTree[i].check();
        i=i+1;ID=ID+1;
    }
    bTree.finalise();
    return bTree;
}
public void displayAll(Tree bTree){
    System.out.println("Running a Full Analysis on the Binary Tree");
    System.out.println("Printing nodes Details");
    for(int i=0;i<bTree.count;i++){
        System.out.println("Node #"+i);
        System.out.println("PrimaryRoot                 :"+bTree.binaryTree[i].isRootPrimary);
        System.out.println("isRoot                      :"+bTree.binaryTree[i].isRoot);
        System.out.println("Data                        :"+bTree.binaryTree[i].Data);
        System.out.println("Number of Children Nodes    :"+bTree.binaryTree[i].childrenNodeCount);
        System.out.println("hasLeft                     :"+bTree.binaryTree[i].hasLeft);
        if(bTree.binaryTree[i].hasLeft)
            System.out.println("LeftNodeID                  :"+bTree.binaryTree[i].leftNodeID);
        System.out.println("hasRight                    :"+bTree.binaryTree[i].hasRight);
        if(bTree.binaryTree[i].hasRight)
            System.out.println("RightNodeID             :"+bTree.binaryTree[i].rightNodeID);
        System.out.println("parentID                    :"+bTree.binaryTree[i].fetchRoot());
        System.out.println("SiblingPairs (if any)       :"+bTree.binaryTree[i].fetchSiblingID());
        System.out.println("____________________________________________________________________________");
    }
    System.out.println("Tree Specifications");
    System.out.println("Total No. of Nodes              :"+bTree.count);
    System.out.println("Height of Tree                  :"+bTree.height);
    System.out.println("Depth of Tree                   :"+bTree.depth);
    System.out.println("Leaves                          :"+bTree.leaves);
    System.out.println("Sibling Pairs                   :"+bTree.siblingPairs);
}
}

主类

package binaryTree;

public class main {
public static void main(String Args[]){
    framework Framework=new framework();
    Tree binaryTree=Framework.intialize();
    Framework.displayAll(binaryTree);
}
}

Answer 1

您的问题在这里:

binaryTree=new node[count];

这只会创建一个新但空数组。

您首先必须迭代该数组并在每个槽中插入一个 Node 对象!

此外:您想阅读有关 Java 编码风格指南的内容。例如，类名总是以大写开头。