使用StreamAPIJava決議文本檔案

我有這個檔案要處理，我試圖弄清楚如何將第二行作為不同的物件讀取。在行的末尾，最后一項是公共汽車的數量。第二行、第四行等應包含 idBus 和 noOfBus，以逗號分隔。

1,Harvard University,2
1,140,2,56
2,Massachusetts Institute of Technology,2
1,240,5,56
3,University of California Berkeley,3
1,112,2,56,3,28
4,Columbia University,4
1,84,2,84,3,84,7,28

基于這些類

 class University {
    public int idUniversity;
    public String nameOfUniversity;
    public int noOfBuses;
 }

 class Bus {
    public int idBus;
    public int noOfBus;
 }

我想要一個函式來處理 CSV 檔案中所有公共汽車和大學線路的串列。它必須使用 Stream API。我不知道這是否可能或如何進行。

當然，可以根據類進行更改，但保留變數而不添加任何額外內容。

我認為最方便的方法是瀏覽檔案并根據兩個類（大學和公共汽車）獲取兩個串列，最后將它們添加到第三個串列中，然后進行處理，但我不知道如何處理。

基于此檔案，我必須使用 Stream API 進行處理，例如“按 ID 排序巴士”或“哪些大學有更多巴士？” 或“哪輛公共汽車去幾所大學？”。

這就是我一直在嘗試做的。通常這就是我瀏覽 CSV 檔案的方式。

private static List<University> readListOfUniversities() throws IOException {
    try (BufferedReader bufferedReader = new BufferedReader(new FileReader(PATH_UNIVERSITIES_TEXT_FILE))) {
        return bufferedReader.lines().map(line -> {
            String[] tokens = line.split(",");
            var idUniversity = Integer.parseInt(tokens[0]);
            var nameOfUniversity = tokens[1].trim();
            var noOfBuses = Integer.parseInt(tokens[2]);
            var university = new University(idUniversity, nameOfUniversity, noOfBuses);
            return university;
        }).collect(Collectors.toList());
    }
}

像這個：

1,Harvard University,2
2,Massachusetts Institute of Technology,2
3,University of California Berkeley,3
4,Columbia University,4

uj5u.com熱心網友回復：

這是我的做法（我對你的課程做了一些修改）

public class University {
    private int id;
    private String name;
    private List<Bus> busList;
    //let the constructor do the work
    public University(String [] data, List<Bus> busList) {
        id = Integer.parseInt(data[0]);
        name = data[1];
        this.busList = busList; 
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public List<Bus> getBusList() {
        return busList;
    }

    @Override
    public String toString() {
        return "University [id="   id   ", name="   name   ", busList="   busList   "]";
    }
    
}

public class Bus {
    private int id;
    private int num;
    
    public Bus(int id, int num) {
        this.id = id;
        this.num = num;
    }
    
    public int getId() {
        return id;
    }

    public int getNum() {
        return num;
    }
    //Method to parse the data into usuable objects
    public static List<Bus> generateBusInfo(String [] data) {
        List<Bus> buses = new ArrayList<>();
        for (int i = 0; i < data.length-1; i =2) {
            int id = Integer.parseInt(data[i]);
            int num = Integer.parseInt(data[i 1]);
            buses.add(new Bus(id, num));
        }
        return buses;
    }

    @Override
    public String toString() {
        return "Bus [id="   id   ", num="   num   "]";
    }
}


public static void main(String[] args) throws IOException {
    //This is just so I dont have to bother with creating a file.
    String input = "1,Harvard University,2\n"   
            "1,140,2,56\n"   
            "2,Massachusetts Institute of Technology,2\n"   
            "1,240,5,56\n"   
            "3,University of California Berkeley,3\n"   
            "1,112,2,56,3,28\n"   
            "4,Columbia University,4\n"   
            "1,84,2,84,3,84,7,28\n";
    List<University> universities = new ArrayList<>();
    //replace StringReader with a FileReader to the path of your file.
    try(BufferedReader reader = new BufferedReader(new StringReader(input))) {
        //read the first line
        String line = reader.readLine();
        while (line != null) { //keep reading until you're done
            String [] uniData = line.split(","); //convert string into an array
            line = reader.readLine(); //read the next line
            if (line != null) {
                String [] busData = line.split(","); //convert
                List<Bus> busList = Bus.generateBusInfo(busData); //make busses
                universities.add(new University(uniData, busList)); //create university and add it to the list
                line = reader.readLine(); //read the next line
            }
        }
    }
    
    //output the list
    for (University uni : universities) {
        System.out.println(uni);
    }
}

您還可以將 Universities 和 buss 讀入Maps 以便于訪問。

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