Customer.java

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

public class Customer implements Serializable {

    private String customerId;
    private String name;
    private String pin;
    private List<Account> accounts;

    public Customer(String customerId, String name, String pin) {
        this.customerId = customerId;
        this.name = name;
        this.pin = pin;
        this.accounts = new ArrayList<>();
    }

    public String getCustomerId() {
        return customerId;
    }

    public String getName() {
        return name;
    }

    public boolean authenticate(String inputPin) {

        if (pin.equals(inputPin)) {
            return true;
        }

        return false;
    }

    public void addAccount(Account account) {
        accounts.add(account);
    }

    public Account getAccount(String accNo) {
        for (Account acc : accounts)
            if (acc.getAccountNumber().equals(accNo))
                return acc;
        return null;
    }

    public void printAccounts() {
        if (accounts.isEmpty()) {
            System.out.println("No accounts available.");
            return;
        }

        for (Account acc : accounts)
            System.out.println("Account: " + acc.getAccountNumber()
                    + " | Balance: " + acc.getBalance());
    }
}