带有自己制造的盒子的Java哈希映射？

Question

我在运行我的代码时遇到问题。它旨在通过包含数据的文件实现框图。我首先把盒子的名称和重量放在一起，然后在该程序中运行另一个程序，增加了盒子之间的关系。文件的

例子：

5 
a 2 
b 1 
c 1 
d 3 
e 2 
3 
a b 
a d 
b c 

代码：

package myutil; 
import java.io.File; 
import java.io.FileNotFoundException; 
import java.util.HashMap; 
import java.util.Scanner; 

public class MyReader { 
public MyReader() { 

} 

public static void addData(String currentFile, HashMap<String, Box> oordnadMap) throws FileNotFoundException{ 



     File file = new File (currentFile); 
     Scanner scanner = new Scanner (file); 

     int iterator = Integer.parseInt(scanner.nextLine()); 
     for(int i = 1; i <= iterator; i++){ 
      Box temp = new Box(scanner.next(), Integer.parseInt(scanner.next())); 
      System.out.println(temp.getName()); 
      System.out.println(temp.getSize()); 
      oordnadMap.put(temp.getName(), temp); 

     } 
     addRelation(oordnadMap, scanner); 



} 

public static void addRelation(HashMap<String, Box> oordnadMap, Scanner scanner)throws FileNotFoundException{ 

    int numerOfRelations = scanner.nextInt(); 
    System.out.println(numerOfRelations); 
    for (int i = 1; i <= numerOfRelations; i++){ 
     String left =scanner.next(); 
     String right = scanner.next(); 
     Box Box1 = oordnadMap.get(left); 
     Box Box2 = oordnadMap.get(right); 
     System.out.println(Box1); 
     System.out.println(Box2); 
     Box2.setTop(Box1); 
     Box1.setBottom(Box2); 
    } 



} 
public static void main (String[] args){ 
    HashMap<String, Box> oordnadMap = new HashMap<String,Box>(); 
    try { 
     String currentFile="boxes1.txt"; 
     addData(currentFile, oordnadMap); 
    } catch (FileNotFoundException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 
} 
} 

我也是在另一个类中指定的盒子：

package myutil; 

import java.util.ArrayList; 

public class Box { 

    private String name; 
    private int Size; 
    ArrayList<Box> top; 
    ArrayList<Box> bottom; 



    public Box(String name, int Size){ 
     this.setName(name); 
     this.setSize(Size); 
    } 


    public void RemoveBox(String name, int Size){ 

    } 

    public void setName(String name) { 
     this.name = name; 
    } 

    public void setSize(int size) { 
     Size = size; 
    } 

    public void setTop (Box temp){ 
     this.top.add(temp); 

    } 

    public void setBottom (Box temp){ 
     this.bottom.add(temp); 
    } 




    public String getName() { 
     return name; 
    } 
    public int getSize() { 
     return Size; 
    } 


} 

当我运行它，我得到的错误：

Exception in thread "main" java.lang.NullPointerException 
at myutil.Box.setTop(Box.java:33) 
at myutil.MyReader.addRelation(MyReader.java:44) 
at myutil.MyReader.addData(MyReader.java:27) 
at myutil.MyReader.main(MyReader.java:55) 

有什么想法？

Answer 1

您在Box类中没有初始化top或bottom，所以Java给了它们一个默认值null。

初始化它们。

public Box(String name, int Size){ 
    this.setName(name); 
    this.setSize(Size); 
    top = new ArrayList<Box>(); 
    bottom = new ArrayList<Box>(); 
}