尝试从 File 读取时出现 java.lang.ArrayIndexOutOfBoundsException

Question

所以基本上我得到了一个问题：

创建将读取 members.txt 文件内容的程序。成员必须分为 3 个阵列，每个团队一个。处理完所有成员后，向终端输出每个团队有多少成员以及团队队长的姓名的信息。文件值以逗号分隔，具有以下架构：

first_name, last_name, team_name, is_captain

这是我想出的代码（关于效率的问题，因为我还是个新手）：

package ssst.edu.ba;

import java.util.ArrayList;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner("members.txt");
        int rcount = 0, bcount = 0, gcount = 0;
        ArrayList<Student> red = new ArrayList<Student>(5);
        ArrayList<Student> blue = new ArrayList<Student>(5);
        ArrayList<Student> green = new ArrayList<Student>(5);
        String line;
        String rCap = "";
        String bCap = "";
        String gCap = "";

        while ((line = scan.nextLine()) != null) {
            String[] obj = line.split(", ");
            if(obj[2] == "Red") {
                Student a = new Student(obj[0],obj[1],obj[2],Boolean.parseBoolean(obj[3]));
                red.add(a);
                rcount++;
                if(obj[3] == "true") {
                    rCap = obj[0] + obj[1];
                }
            }
            else if (obj[2] == "Blue") {
                Student a = new Student(obj[0],obj[1],obj[2],Boolean.parseBoolean(obj[3]));
                blue.add(a);
                bcount++;
                if(obj[3] == "true") {
                    bCap = obj[0] + obj[1];
                }
            }
            else {
                Student a = new Student(obj[0],obj[1],obj[2],Boolean.parseBoolean(obj[3]));
                green.add(a);
                gcount++;
                if(obj[3] == "true") {
                    gCap = obj[0] + obj[1];
                }
            }
        }
        System.out.println("There are " + rcount + " people on the red team.");
        System.out.println("There are " + bcount + " people on the blue team.");
        System.out.println("There are " + gcount + " people on the green team.");
        System.out.println("The captain for the red team is: " + rCap);
        System.out.println("The captain for the blue team is: " + bCap);
        System.out.println("The captain for the green team is: " + gCap);
    }
}

“Student”类很简单，它有 3 个私有 String 属性和一个私有 bool 值，它还有一个带有 4 个参数的构造函数，用于将值设置为文本文档“members.txt”中给出的值

文本文档如下所示：

Ginny, Gullatt, Blue, false
Tiara, Curd, Red, false
Camie, Poorman, Green, false
Jammie, Hasson, Green, false
Lionel, Hailey, Blue, false
Genevive, Mckell, Red, true
Esteban, Slaubaugh, Blue, false
Elden, Harte, Red, false
Tasia, Rodrigue, Green, false
Nathanial, Dentler, Red, false
Valda, Nicoletti, Blue, false
Kary, Wilkerson, Green, false
Coletta, Akey, Blue, false
Wilmer, Jack, Red, false
Loreta, Agnew, Green, true
Suzy, Cleveland, Red, false
Pasty, Laprade, Blue, false
Candie, Mehaffey, Green, false
Glady, Landman, Blue, true
Tierra, Mckeown, Red, false
Glady, Laprade, Green, false

问题：我收到此异常消息

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 2 out of bounds for length 1

我不知道这是否与 ArrayList 或字符串数​​组“obj”相关联，我也不知道如何修复它。

Answer 1

要将 Scanner 与文件一起使用，您必须通过 File 类提供文件，如下所示：

import java.io.File;
import java.io.FileNotFoundException;

public static void main(String[] args) throws FileNotFoundException {
    Scanner scan = new Scanner(new File("./members.txt"));

    /* ...Some code */
}

实际上，您正在从只包含文本“members.txt”的流中读取

扫描器（字符串源）

构造一个新的扫描器，生成从指定字符串扫描的值。

所以你正在使用构造函数 htat 接收一个字符串作为参数，而不是使用文件的那个。看https://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#Scanner(java.lang.String)

您还必须使用hasNextLine 函数，例如：

while (scan.hasNextLine()) {
    line = scan.nextLine();

/* some code */

}

否则你会得到异常java.util.NoSuchElementException

这是您的程序的工作版本：

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Scanner;
import java.io.File;
import java.io.FileNotFoundException;

public class Main {

    public static void main(String[] args) throws FileNotFoundException {
        Scanner scan = new Scanner(new File("./members.txt"));

        ArrayList<Student> red = new ArrayList<Student> (5);
        ArrayList<Student> blue = new ArrayList<Student> (5);
        ArrayList<Student> green = new ArrayList<Student> (5);

        // we use a map to save the index where is the captain in the array list
        HashMap<String,Integer> captains = new HashMap <String, Integer> ();

        while (scan.hasNextLine()) {
            String[] rawStudent = scan.nextLine().split(", ");
            Student student = new Student(rawStudent);

            ArrayList selectedTeam = red;

            // we select dynamically the list where the student will be added
            switch (student.getTeam()) {
                case "Red": selectedTeam = red; break;
                case "Blue": selectedTeam = blue; break;
                case "Green": selectedTeam = green; break;
            }

            selectedTeam.add(student);

            if (student.isCaptain()) {
                int lastAddedIndex = selectedTeam.size() - 1;

                captains.put(student.getTeam(), lastAddedIndex);
            }
        }

        System.out.println("There are " + red.size() + " people on the red team.");
        System.out.println("There are " + blue.size() + " people on the blue team.");
        System.out.println("There are " + green.size() + " people on the green team.");

        System.out.println("The captain for the red team is: " + red.get(captains.get("Red")).getFullName());
        System.out.println("The captain for the blue team is: " + blue.get(captains.get("Blue")).getFullName());
        System.out.println("The captain for the green team is: " + green.get(captains.get("Green")).getFullName());
    }
}

class Student {
    private String name;
    private String lastName;
    private String team;
    private boolean isCaptain;

    public Student(String p1, String p2, String p3, boolean p4) {
        this.name = p1;
        this.lastName = p2;
        this.team = p3;
        this.isCaptain = p4;
    }

    public Student(String[] list) {
        this(list[0], list[1], list[2], Boolean.parseBoolean(list[3]));
    }

    public String getFullName() {
        return this.name + " " + this.lastName;
    }

    public boolean isCaptain() {
        return this.isCaptain;
    }

    public String getTeam() {
        return this.team;
    }
}

希望对你有帮助。

Answer 2

我已经制作了一个与此类似的程序，其中我正在读取不同格式的文件，例如 CSV EXCEL 等并对其执行操作，因此您可以检查代码是行业级代码，并且会提供更多曝光而不是只为您的解决方案。

https://github.com/NahidAkhter/feeCalculator.git

简而言之，我可以在下面给出一个 sn-p 1) TextTransctionReader.java

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

import com.feecalculator.Constant.FILETYPE;
import com.feecalculator.Transaction;


public class TextTransctionReader extends AbstractTransactionReader implements ITransactionManager {


    @Override
    public void readTransaction(File transactionFile) {


        BufferedReader br = null;
        String line = "";
        String cvsSplitBy = ",";

        try {

            br = new BufferedReader(new FileReader(transactionFile));
            while ((line = br.readLine()) != null) {
                String[] transactionAttributes = line.split(cvsSplitBy);
                Transaction transaction = getTransaction(transactionAttributes); 
                saveTransaction(transaction);

            }        
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (br != null) {
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    @Override
    public ITransactionManager readFile(FILETYPE fileType) {
        if(fileType == FILETYPE.TEXT){
            return TrasactionReader.getTrasactionReaderInstance().readTextFile();
        }
        return null;
    }


}

主类如下：

import java.io.File;

import com.feecalculator.Constant.FILETYPE;
import com.feecalculator.reader.ITransactionManager;
import com.feecalculator.reader.TrasactionReader;


public class MainFeeCalculator {
    public static void main(String[] args) {

        File transactionfile = new File(new File("").getAbsolutePath(),"resource/Input_java.xlsx");
        ITransactionManager tranction= TrasactionReader.getTrasactionReaderInstance().readFile(FILETYPE.EXCEL,transactionfile);     
        tranction.displayTransactionReport();   


    }
}

希望这能解决您的问题。