来源:Medium 今天我们将为银行系统开发一个简单的 Java 应用程序。它将帮助我们更好地理解 OOP 概念如何在 Java 程序中使用。 首先,我们需要在计算机上安装Java环境,最好是Java 11。接下来,我们将详细介绍控制台应用程序的功能。 功能性:
- 创建一个帐户;
- 输入退出;
- 显示最近5笔交易;
- 现金存款;
- 显示当前用户信息。
- 遗产;
- 多态性;
- 封装。
应用开发
让我们在 Eclipse 或 IntelliJ IDEA 中创建一个新的 Java 项目。让我们定义一个名为SavingsAccount的新接口。public interface SavingsAccount {
void deposit(double amount, Date date);
}
我已经实现了一个托管存款方法的接口。每次我向支票账户充值时都会调用此方法。这里使用的 OOP 概念是多态性(接口中的方法没有主体)。通过重写具有相同名称和参数的方法,可以在Customer类中找到此方法的实现。这样,您就可以在子类中重写父接口中的方法。然后我们需要客户向支票账户存钱。但首先,让我们定义我们的Customer类。
public class Customer extends Person implements SavingsAccount {
private String username;
private String password;
private double balance;
private ArrayList<String> transactions = new ArrayList<>(5);
public Customer(String firstName, String lastName, String address, String phone, String username, String password, double balance, ArrayList<String> transactions, Date date) {
super(firstName, lastName, address, phone);
this.username = username;
this.password = password;
this.balance = balance;
addTransaction(String.format("Initial deposit - " + NumberFormat.getCurrencyInstance().format(balance) + " as on " + "%1$tD" + " at " + "%1$tT.", date));
}
private void addTransaction(String message) {
transactions.add(0, message);
if (transactions.size() > 5) {
transactions.remove(5);
transactions.trimToSize();
}
}
//Getter Setter
public ArrayList<String> getTransactions() {
return transactions;
}
@Override
public void deposit(double amount, Date date) {
balance += amount;
addTransaction(String.format(NumberFormat.getCurrencyInstance().format(amount) + " credited to your account. Balance - " + NumberFormat.getCurrencyInstance().format(balance) + " as on " + "%1$tD" + " at " + "%1$tT.", date));
}
@Override
public String toString() {
return "Customer{" +
"username='" + username + '\'' +
", password='" + password + '\'' +
", balance=" + balance +
", transactions=" + transactions +
'}';
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Customer customer = (Customer) o;
if (Double.compare(customer.getBalance(), getBalance()) != 0) return false;
if (getUsername() != null ? !getUsername().equals(customer.getUsername()) : customer.getUsername() != null)
return false;
if (getPassword() != null ? !getPassword().equals(customer.getPassword()) : customer.getPassword() != null)
return false;
return getTransactions() != null ? getTransactions().equals(customer.getTransactions()) : customer.getTransactions() == null;
}
@Override
public int hashCode() {
int result;
long temp;
result = getUsername() != null ? getUsername().hashCode() : 0;
result = 31 * result + (getPassword() != null ? getPassword().hashCode() : 0);
temp = Double.doubleToLongBits(getBalance());
result = 31 * result + (int) (temp ^ (temp >>> 32));
result = 31 * result + (getTransactions() != null ? getTransactions().hashCode() : 0);
return result;
}
这里使用的 OOP 概念是继承,因为Customer类从Person类接收属性。也就是说,Person类的几乎所有属性都是继承的,并且父子关系从Person到Customer都是可见的。现在我们需要一个具有两个类的所有属性的构造函数,并添加一个 superconstructor 关键字来指定继承的属性。在实现SavingsAccount接口时,我们必须重写Customer类中的Deposit方法。为此,我们将在此类中编写该方法的实现。此外,交易列表被初始化以显示最后五笔交易。构造函数调用addTransaction方法,该方法显示更改日期和已完成的事务。
private void addTransaction(String message) {
transactions.add(0, message);
if (transactions.size() > 5) {
transactions.remove(5);
transactions.trimToSize();
}
}
现在我们来谈谈父类Person。
public class Person {
private String firstName;
private String lastName;
private String address;
private String phone;
public Person() {}
public Person(String firstName, String lastName, String address, String phone) {
this.firstName = firstName;
this.lastName = lastName;
this.address = address;
this.phone = phone;
}
//Getters Setters
@Override
public String toString() {
return "Person{" +
"firstName='" + firstName + '\'' +
", lastName='" + lastName + '\'' +
", address='" + address + '\'' +
", phone='" + phone + '\'' +
'}';
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Person person = (Person) o;
if (getFirstName() != null ? !getFirstName().equals(person.getFirstName()) : person.getFirstName() != null)
return false;
if (getLastName() != null ? !getLastName().equals(person.getLastName()) : person.getLastName() != null)
return false;
if (getAddress() != null ? !getAddress().equals(person.getAddress()) : person.getAddress() != null)
return false;
return getPhone() != null ? getPhone().equals(person.getPhone()) : person.getPhone() == null;
}
@Override
public int hashCode() {
int result = getFirstName() != null ? getFirstName().hashCode() : 0;
result = 31 * result + (getLastName() != null ? getLastName().hashCode() : 0);
result = 31 * result + (getAddress() != null ? getAddress().hashCode() : 0);
result = 31 * result + (getPhone() != null ? getPhone().hashCode() : 0);
return result;
}
在Person类中,我们通过对每个属性应用private访问修饰符来使用封装的概念。Java 中的封装可以定义为一种机制,通过该机制将操作这些数据的方法组合成一个单元。本质上,来自 Person 类的数据仅在该类中可用,而在其他类或包中不可用。最后,我们的主类,称为Bank。这是我们运行应用程序并与所有类的功能进行交互的主类。
public class Bank {
private static double amount = 0;
Map<String, Customer> customerMap;
Bank() {
customerMap = new HashMap<String, Customer>();
}
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
Customer customer;
Bank bank = new Bank();
int choice;
outer:
while (true) {
System.out.println("\n-------------------");
System.out.println("BANK OF JAVA");
System.out.println("-------------------\n");
System.out.println("1. Registrar cont.");
System.out.println("2. Login.");
System.out.println("3. Exit.");
System.out.print("\nEnter your choice : ");
choice = sc.nextInt();
sc.nextLine();
switch (choice) {
case 1:
System.out.print("Enter First Name : ");
String firstName = sc.nextLine();
System.out.print("Enter Last Name : ");
String lastName = sc.nextLine();
System.out.print("Enter Address : ");
String address = sc.nextLine();
System.out.print("Enter contact number : ");
String phone = sc.nextLine();
System.out.println("Set Username : ");
String username = sc.next();
while (bank.customerMap.containsKey(username)) {
System.out.println("Username already exists. Set again : ");
username = sc.next();
}
System.out.println("Set a password:");
String password = sc.next();
sc.nextLine();
customer = new Customer(firstName, lastName, address, phone, username, password, new Date());
bank.customerMap.put(username, customer);
break;
case 2:
System.out.println("Enter username : ");
username = sc.next();
sc.nextLine();
System.out.println("Enter password : ");
password = sc.next();
sc.nextLine();
if (bank.customerMap.containsKey(username)) {
customer = bank.customerMap.get(username);
if (customer.getPassword().equals(password)) {
while (true) {
System.out.println("\n-------------------");
System.out.println("W E L C O M E");
System.out.println("-------------------\n");
System.out.println("1. Deposit.");
System.out.println("2. Transfer.");
System.out.println("3. Last 5 transactions.");
System.out.println("4. User information.");
System.out.println("5. Log out.");
System.out.print("\nEnter your choice : ");
choice = sc.nextInt();
sc.nextLine();
switch (choice) {
case 1:
System.out.print("Enter amount : ");
while (!sc.hasNextDouble()) {
System.out.println("Invalid amount. Enter again :");
sc.nextLine();
}
amount = sc.nextDouble();
sc.nextLine();
customer.deposit(amount, new Date());
break;
case 2:
System.out.print("Enter beneficiary username : ");
username = sc.next();
sc.nextLine();
System.out.println("Enter amount : ");
while (!sc.hasNextDouble()) {
System.out.println("Invalid amount. Enter again :");
sc.nextLine();
}
amount = sc.nextDouble();
sc.nextLine();
if (amount > 300) {
System.out.println("Transfer limit exceeded. Contact bank manager.");
break;
}
if (bank.customerMap.containsKey(username)) {
Customer payee = bank.customerMap.get(username); //Todo: check
payee.deposit(amount, new Date());
customer.withdraw(amount, new Date());
} else {
System.out.println("Username doesn't exist.");
}
break;
case 3:
for (String transactions : customer.getTransactions()) {
System.out.println(transactions);
}
break;
case 4:
System.out.println("Titularul de cont cu numele: " + customer.getFirstName());
System.out.println("Titularul de cont cu prenumele : " + customer.getLastName());
System.out.println("Titularul de cont cu numele de utilizator : " + customer.getUsername());
System.out.println("Titularul de cont cu addresa : " + customer.getAddress());
System.out.println("Titularul de cont cu numarul de telefon : " + customer.getPhone());
break;
case 5:
continue outer;
default:
System.out.println("Wrong choice !");
}
}
} else {
System.out.println("Wrong username/password.");
}
} else {
System.out.println("Wrong username/password.");
}
break;
case 3:
System.out.println("\nThank you for choosing Bank Of Java.");
System.exit(1);
break;
default:
System.out.println("Wrong choice !");
}}}}
使用java.util库,我们调用Scanner来读取键盘。通过通过其定义(称为Bank )转换Customer对象,我们创建了一个Bank()类型的新对象。一段时间后,我们将显示开始菜单。使用nextLine时,会读取从键盘添加的数字。下面我们有一个新的构造函数来保存我们的地图,即客户端数据。Map.put用于保存或更新客户数据。客户=新客户(名字,姓氏,地址,电话,用户名,密码,新日期());
bank.customerMap.put(username, customer);
如果有连接,我们会得到一个带有选项的新菜单。相同的方法通过使用while和switch来调用应用程序功能。第 1 阶段:向您的活期账户充值。步骤2:显示最近5笔交易。第三阶段:我们将客户端数据从卡输出到控制台。第四阶段:关闭菜单。可以在此处找到该程序的源代码。我希望这个例子能够帮助您更加熟悉 Java 中 OOP 概念的使用。
GO TO FULL VERSION