根据类图，实现java代码：@startuml class BankAccount { -accountNumber : String -balance : double -ownerName : String +BankAccount(accountNumber:String, ownerName:String) +getAccountNumber():String +getBalance():double +getOwnerName():String +deposit(amount:double):void +withdraw(amount:double):void } class BankAccountDAO { -accounts : Map<String, BankAccount> -fileName : String +BankAccountDAO(fileName:String) +getAccount(accountNumber:String):BankAccount +getAllAccounts():List<BankAccount> +addAccount(account:BankAccount):void +updateAccount(account:BankAccount):void +deleteAccount(accountNumber:String):void -saveToFile():void } BankAccount -> BankAccountDAO @enduml

public class BankAccount {
    private String accountNumber;
    private double balance;
    private String ownerName;

    public BankAccount(String accountNumber, String ownerName) {
        this.accountNumber = accountNumber;
        this.ownerName = ownerName;
        this.balance = 0.0;
    }

    public String getAccountNumber() {
        return accountNumber;
    }

    public double getBalance() {
        return balance;
    }

    public String getOwnerName() {
        return ownerName;
    }

    public void deposit(double amount) {
        balance += amount;
    }

    public void withdraw(double amount) {
        balance -= amount;
    }
}

import java.io.*;
import java.util.*;

public class BankAccountDAO {
    private Map<String, BankAccount> accounts;
    private String fileName;

    public BankAccountDAO(String fileName) {
        this.fileName = fileName;
        accounts = new HashMap<String, BankAccount>();
        loadFromFile();
    }

    public BankAccount getAccount(String accountNumber) {
        return accounts.get(accountNumber);
    }

    public List<BankAccount> getAllAccounts() {
        return new ArrayList<BankAccount>(accounts.values());
    }

    public void addAccount(BankAccount account) {
        accounts.put(account.getAccountNumber(), account);
        saveToFile();
    }

    public void updateAccount(BankAccount account) {
        accounts.put(account.getAccountNumber(), account);
        saveToFile();
    }

    public void deleteAccount(String accountNumber) {
        accounts.remove(accountNumber);
        saveToFile();
    }

    private void loadFromFile() {
        try {
            BufferedReader reader = new BufferedReader(new FileReader(fileName));
            String line;
            while ((line = reader.readLine()) != null) {
                String[] parts = line.split(",");
                String accountNumber = parts[0];
                String ownerName = parts[1];
                double balance = Double.parseDouble(parts[2]);
                BankAccount account = new BankAccount(accountNumber, ownerName);
                account.deposit(balance);
                accounts.put(accountNumber, account);
            }
            reader.close();
        } catch (IOException e) {
            System.out.println("Failed to load accounts from file: " + e.getMessage());
        }
    }

    private void saveToFile() {
        try {
            BufferedWriter writer = new BufferedWriter(new FileWriter(fileName));
            for (BankAccount account : accounts.values()) {
                String line = account.getAccountNumber() + "," + account.getOwnerName() + "," + account.getBalance();
                writer.write(line);
                writer.newLine();
            }
            writer.close();
        } catch (IOException e) {
            System.out.println("Failed to save accounts to file: " + e.getMessage());
        }
    }
}