不应到达的 split() 上的空指针

Question

所以我正在从 .txt 文件中读取 bikeParts 列表。那部分工作正常。问题是我的缓冲 reader 有一个 while 循环，它应该检查下一行是否为空。该程序循环遍历 .txt 文件中的每个 aprt，然后尝试读取额外的 "null" 行。我很困惑为什么程序没有退出 while 循环。

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

这是一个 .FXML 项目，所以还有更多类，但这是目前我遇到问题的唯一一个。为什么它会经历那个 while 循环？我运行程序处于调试模式，在最后运行通过时，line = null，这会导致 split 调用出现空指针。但它不应该达到那个 split()

Answer 1

好吧，如果不编译你的代码，我 99.9% 确定错误出在第二次 readLine() 调用上，你的 while 条件是 (line = br.readLine()) != null，这意味着你正在读取一行并将其分配给变量 line然后检查该行是否为空。在那之后，出于某种原因，您正在阅读 nextLine() 并且您“丢弃”上一行。因此，如果您从 txt 文件中读取最后一行，则 while 条件将为真，您将从文件设置 line = null 中再次读取，因此尝试拆分空字符串将为您提供 NullPointerExpection

为了解决您的问题，只需删除第二个 readLine() 调用

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])));
}

不应到达的 split() 上的空指针

Null pointer on a split() that shouldn't be reached

file-io

split

javafx

while-loop

bufferedreader