從文件中讀取對象並將其保存到 ArrayList

Question

我在從文件中讀取特定對象並將其保存到 ArrayList 時遇到問題。

首先，我使用writeCustomer()編寫一個客戶。 然后我從List customerList寫入所有記錄並將它們保存到文件中。 這很好用。

然后我想讀取保存的文件，所以我使用readCustomer()讀取一行。 此方法返回一個Customer ，然后我想使用readData()返回一個包含所有Clients的列表並讀取它，我在行 list.add(readCustomer(bufferedReader)) 中有 nullPointerException;

我的Class Customer有一個構造函數，並且有一個覆蓋方法toString() 。

public class SaveCustomers {

public static void main(String[] args) throws IOException {

    List<Customers> customersList = new ArrayList<>();
    customersList.add(new Customers("ABC", 10));
    customersList.add(new Customers("SGS", 20));
    customersList.add(new Customers("FSD", 30));

    try (PrintWriter out = new PrintWriter("customer.txt", "UTF-8"))
    {         writeData(customersList, out);      }


    BufferedReader bufferedReader = new BufferedReader(new FileReader("customer.txt"));
    List<Customers> newList =  readData(bufferedReader);


    for(Customers c: newList){
        System.out.println(c);
    }
}

private static void writeCustomer(PrintWriter out, Customers customers){
    out.println(customers.getName()+"|"+customers.getTarrif());
}

private static void writeData(List<Customers> customersList, PrintWriter out){
    for(Customers c:customersList){
        writeCustomer(out, c);
    }
}

public static Customers readCustomer(BufferedReader bufferedReader) throws IOException {
    String line = bufferedReader.readLine();
    String [] tokens = line.split("\\|");
    String name = tokens[0];
    int time = Integer.valueOf(tokens[1]);
    return new Customers(name, time);
}

public static List<Customers> readData(BufferedReader bufferedReader) throws IOException {

    List<Customers> list = new ArrayList<>();
        while (bufferedReader.readLine() != null) {
            list.add(readCustomer(bufferedReader));
        }
    return list;
}}

Answer 1

您已經接近解決方案了；)

在方法中：

readData(BufferedReader bufferedReader)

只需改變這一行

for(Customers l : list) {

到這個：

while (bufferedReader.ready()) {