如何从文件中读取信息并将信息存储在链表（Java）中？

Question

我正在尝试读取包含创建手机的属性（例如序列号、品牌、年份和价格）的文件。然后，我想将信息存储在变量中，以便可以使用其构造函数创建 CellPhone 对象。之后我需要继续在链接列表中添加这些 CellPhone 对象，同时确保没有重复项（具有相同序列号的 CellPhone 对象）。它适用于 List 为空的第一种情况，但是在我将第一个对象添加到 List 之后，就会出现 NoSuchElementException。我做错了什么，如何正确读取文件？任何帮助表示赞赏。

CellListUtilization 类：

// Method to read the file and store the information in the CellList
public static void processFile(Scanner sc1, CellList cl1) {
    String S = null;

    while(sc1.hasNext())
    {
        // First case where the list is empty
        if (cl1.getSize() == 0)
        {
            S = sc1.next();
            serialNum = Long.parseLong(S);
            S = sc1.next();
            brand = S;
            S = sc1.next();
            price = Double.parseDouble(S);
            S = sc1.next();
            year = Integer.parseInt(S);

            CellPhone c1 = new CellPhone(serialNum, brand, year, price);
            cl1.addToStart(c1);
        }
        else
        {
            serialNum = Long.parseLong(S);
            S = sc1.next();
            brand = S;
            S = sc1.next();
            price = Double.parseDouble(S);
            S = sc1.next();
            year = Integer.parseInt(S);

            if (!(cl1.contains(serialNum)))
            {
                CellPhone c2 = new CellPhone(serialNum, brand, year, price);
                cl1.addToStart(c2);
            }
        }
        S = sc1.next();
    }
}

我要读取的文件：

3890909 Samsung         857.28 2015
2787985 Acer            572.20 2013
4900088 LG              232.99 2017
1989000 Nokia           237.24 2006
0089076 Sharp           564.22 2009
2887685 Motorola        569.28 2012
7559090 Pansonic        290.90 2005
2887460 Siemens         457.28 2009
2887685 Apple           969.28 2018
6699001 Lenovo          237.29 2012
9675654 Nokia           388.00 2009
1119002 Motorola        457.28 2008
5000882 Apple           977.27 2016
8888902 Samsung         810.35 2018
5890779 Motorola        457.28 2007
7333403 BenQ            659.00 2009
2999900 Siemens         457.28 2006
6987612 HTC             577.25 2009
8888902 BenQ            410.35 2009
8006832 Motorola        423.22 2008
5555902 SonyEricsson    177.11 2007
9873330 Nokia           677.90 2010
8888902 BenQ            410.35 2009
5909887 Apple           726.99 2017
2389076 BlackBerry      564.22 2010
1119000 SonyEricsson    347.94 2009

Answer 1

您也可以简单地查看它以避免重复

像这样声明手机

public class CellPhone {

    private Long serialNumber;
    private String brand;
    private Integer year;
    private Double price;

    CellPhone(Long serialNumber, String brand, int year, double price) {
        this.serialNumber = serialNumber;
        this.brand = brand;
        this.year = year;
        this.price = price;
    }

    public Long getSerialNumber() {
        return serialNumber;
    }

    public void setSerialNumber(Long serialNumber) {
        this.serialNumber = serialNumber;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public Integer getYear() {
        return year;
    }

    public void setYear(Integer year) {
        this.year = year;
    }

    public Double getPrice() {
        return price;
    }

    public void setPrice(Double price) {
        this.price = price;
    }

    @Override
    public int hashCode() {
        return serialNumber.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof CellPhone))
            return false;

        CellPhone mdc = (CellPhone) obj;
        return mdc.serialNumber.equals(serialNumber);
    }
}

然后你的类需要像这样修改

public class ListPractice {


    public static void main(String[] args) throws IOException {
        //Creating BufferedReader object to read the input text file
        Scanner scanner = new Scanner(new File("E:\\Projects\\JavaBasics\\src\\data.txt"));
        LinkedList<CellPhone> cellPhones = new LinkedList<>();
        processFile(scanner, cellPhones);

        Iterator i = cellPhones.iterator();
        while (i.hasNext()) {
            CellPhone phone = (CellPhone) i.next();
            System.out.println(phone.getSerialNumber());
        }
    }

    public static void processFile(Scanner sc1, LinkedList<CellPhone> cl1) {
        String S = null;

        while (sc1.hasNext()) {

            S = sc1.next();
            Long serialNum = Long.parseLong(S.trim());
            S = sc1.next();
            String brand = S.trim();
            S = sc1.next();
            double price = Double.parseDouble(S.trim());
            S = sc1.next();
            int year = Integer.parseInt(S.trim());

            CellPhone c1 = new CellPhone(serialNum, brand, year, price);
            if (!cl1.contains(c1))
                cl1.add(c1);
           // else System.out.println("Duplicate data");
        }
    }

}

Answer 2

在 while 循环条件可以断言该行存在之前，您的代码正在尝试获取下一行的元素。如果文件在一行中有 4 列数据，则不应在单个循环中调用 sc1.next() 超过 4 次以避免 NoSuchElementException。

将最后一个 sc1.next() 调用从 while 循环的末尾移动到 else 块的开头应该可以解决此问题。

while(sc1.hasNext())
{
    // First case where the list is empty
    if (cl1.getSize() == 0)
    {
        S = sc1.next();
        serialNum = Long.parseLong(S);
        S = sc1.next();
        brand = S;
        S = sc1.next();
        price = Double.parseDouble(S);
        S = sc1.next();
        year = Integer.parseInt(S);

        CellPhone c1 = new CellPhone(serialNum, brand, year, price);
        cl1.addToStart(c1);
    }
    else
    {
        S = sc1.next();
        serialNum = Long.parseLong(S);
        S = sc1.next();
        brand = S;
        S = sc1.next();
        price = Double.parseDouble(S);
        S = sc1.next();
        year = Integer.parseInt(S);

        if (!(cl1.contains(serialNum)))
        {
            CellPhone c2 = new CellPhone(serialNum, brand, year, price);
            cl1.addToStart(c2);
        }
    }
} 

Answer 3

这个问题是因为在 while 结束时您正在执行 sc1.next() 但在循环结束时没有什么可读取的，因此您可以添加一个 if 来解决您的问题。

  public static void processFile(Scanner sc1, CellList cl1) {
        String S = null;

        while(sc1.hasNext())
        {
            // First case where the list is empty
            if (cl1.getSize() == 0)
            {
                S = sc1.next();
                serialNum = Long.parseLong(S);
                S = sc1.next();
                brand = S;
                S = sc1.next();
                price = Double.parseDouble(S);
                S = sc1.next();
                year = Integer.parseInt(S);

                CellPhone c1 = new CellPhone(serialNum, brand, year, price);
                cl1.addToStart(c1);
            }
            else
            {
                serialNum = Long.parseLong(S);
                S = sc1.next();
                brand = S;
                S = sc1.next();
                price = Double.parseDouble(S);
                S = sc1.next();
                year = Integer.parseInt(S);

                if (!(cl1.contains(serialNum)))
                {
                    CellPhone c2 = new CellPhone(serialNum, brand, year, price);
                    cl1.addToStart(c2);
                }
            }
             if(sc1.hasNext()) { 
             S =sc1.next();
            }
        }
    }