不應該到達的split（）上的空指針

Question

所以我從.txt文件讀取bikeParts的列表。這部分工作正常。麻煩的是我有一個while循環用於緩衝讀取器，它應該檢查下一行是否爲空。該程序循環遍歷.txt文件中的每個aprt，但隨後嘗試讀取額外的「空」行。我很困惑，爲什麼程序沒有退出while循環。

package sample; 

import javafx.application.Application; 
import javafx.fxml.FXMLLoader; 
import javafx.scene.Parent; 
import javafx.scene.Scene; 
import javafx.stage.Stage; 
import java.util.*; 
import java.io.*; 
import java.nio.*; 

public class Main extends Application { 
    public static String read(String fileName) { 
     String success="success"; 
     String nope="not found"; 
     String IO="could not read file"; 

     File file = new File(fileName); 
     String line = null; 
     String[] fileNamer = fileName.split(".txt"); 
     String houseName = fileNamer[0].toString(); 
     try { 
      FileReader fr = new FileReader(file); 
      BufferedReader br = new BufferedReader(fr); 
      ArrayList<BikeParts> partList = new ArrayList<>(); 

      while ((line = br.readLine()) != null) { //the while loop in question 
       line = br.readLine(); 
       String[] elements = line.split(","); //null pointer on this line 
       partList.add(new BikeParts(elements[0], (elements[1]), Double.parseDouble(elements[2]), 
         Double.parseDouble(elements[3]), Boolean.parseBoolean(elements[4]), Integer.parseInt(elements[5]))); 
      }//BikeParts is a constructor for each part on the .txt file. makes a part object out of partName, partNumber, listPrice, salesPrice, onSale, and quantity 
      Warehouse house = new Warehouse(houseName, partList); //partList is the ArrayList of parts that is contained within the Warehouse that was just created by the user 
      return success; //debug return statement 
     } catch (FileNotFoundException e) { 
      return nope; //debug return statement 
     } catch (IOException e) { 
      e.printStackTrace(); 
      return IO; //debug return statement 
     } 
    } 

    public void display() { 

    } 

    public void newPart(BikeParts p) { 
     MainWarehouse.add(p); 
    } 

    public void sortMainByName(MainWarehouse houseName) { 


    } 

    public void sortByNumber() { 

    } 

    public void addVan(String vanName, ArrayList<BikeParts> invName) { 
     //Vans.Vans(vanName,invName); 
    } 

    @Override 
    public void start(Stage primaryStage) throws Exception { 
     Parent root = FXMLLoader.load(getClass().getResource("GUI.fxml")); 
     primaryStage.setTitle("Hello World"); 
     primaryStage.setScene(new Scene(root, 800, 800)); 
     primaryStage.show(); 
    } 


    public static void main(String[] args) { 
     launch(args); 
    } 
} 

.txt文件：

26inTube,1234567891,7.00,5.58,true,35 
10spFrontDerailer,1234567897,41.00,31.50,true,10 
seatPost,1234567892,17.00,1.23,true,5 
700-25SwhalbeTire,1234567895,51.00,40.50,true,10 
carbonHandleBars42cm,1234567893,47.00,5.58,true,3 
10spRearDerailuer,1234567896,82.00,70.50,true,10 
11spFrontDerailuer,1234567899,61.00,50.50,true,10 
WTB_saddle,1234567890,33.00,25.58,false,15 
mensBibsMedium,1234567900,110.00,99.00,false,4 
womensHelmetSmall,1234567901,130.00,79.00,false,4 
spdPedals,1234567902,62.31,79.00,true,4 
700-23SwhalbeTire,1234567894,51.00,40.50,true,10 
timePedals,1234567903,102.31,89.00,false,4 
frogPedalsTitanium,1234567904,142.31,130.00,false,4 
11spRearDerailuer,1234567898,97.00,80.50,true,10 
carbonWheelSet,1234567905,542.31,480.00,false,4 
mountainFork29,1234567912,223.00,195.00,false,4 
lynskeyTitaniumFrame265Med,1234567906,2542.99,1880.00,false,2 
grr,1234567907,4567.89,3456.78,false,2 
zarminComputer,1234567908,543.21,480.00,false,2 
womensBibsMedium,1234567909,110.00,99.00,false,4 
womensJacketMedium,1234567911,120.00,95.00,false,4 
mensJacketMedium,1234567910,120.00,95.00,false,4 

這是一個.FXML項目，所以有更多的類，但是這是目前唯一一個我有任何問題。爲什麼它經歷了while循環？我在調試模式下運行程序，並在最後一次運行，line = null，這會導致分割調用上的空指針。但它不應該達到那個分割（）

Answer 1

那麼沒有編譯你的代碼我99.9％確定錯誤是在第二次readLine（）調用，你的while條件是(line = br.readLine()) != null這意味着你正在閱讀一行和你將其分配給變量行，然後檢查該行是否爲空。之後，出於某種原因，您正在閱讀nextLine（），並且'放棄了'的上一行。所以，如果你從txt文件中讀取最後一行，while條件將爲true，並且您將再次從文件設置line = null中讀取，因此嘗試拆分空字符串將會給您一個空指針檢查

爲了解決您的問題，只需刪除第二個readLine（）調用

while ((line = br.readLine()) != null) { 
    String[] elements = line.split(","); 
    partList.add(new BikeParts(elements[0], (elements[1]), Double.parseDouble(elements[2]), 
      Double.parseDouble(elements[3]), Boolean.parseBoolean(elements[4]), Integer.parseInt(elements[5]))); 
}