实验 22：状态模式
本次实验属于模仿型实验，通过本次实验学生将掌握以下内容：
1、理解状态模式的动机，掌握该模式的结构；
2、能够利用状态模式解决实际问题。
[实验任务一]：银行账户
用Java代码模拟实现课堂上的“银行账户”的实例，要求编写客户端测试代码模拟用户存款和取款，注意账户对象状态和行为的变化。
实验要求：
1. 画出对应的类图；
2. 提交源代码；
3. 注意编程规范。
1.
2.// AccountState.java
public interface AccountState {
void deposit(double amount);
void withdraw(double amount);
}
// NormalState.java
public class NormalState implements AccountState {
private BankAccount account;
public NormalState(BankAccount account) {
this.account = account;
}
@Override
public void deposit(double amount) {
account.setBalance(account.getBalance() + amount);
System.out.println("Deposited: " + amount + ", New Balance: " + account.getBalance());
}
@Override
public void withdraw(double amount) {
if (amount <= account.getBalance()) {
account.setBalance(account.getBalance() - amount);
System.out.println("Withdrew: " + amount + ", New Balance: " + account.getBalance());
} else {
System.out.println("Insufficient funds! Current Balance: " + account.getBalance());
account.setState(new OverdrawnState(account));
}
}
}
// OverdrawnState.java
public class OverdrawnState implements AccountState {
private BankAccount account;
public OverdrawnState(BankAccount account) {
this.account = account;
}
@Override
public void deposit(double amount) {
account.setBalance(account.getBalance() + amount);
System.out.println("Deposited: " + amount + ", New Balance: " + account.getBalance());
if (account.getBalance() >= 0) {
account.setState(new NormalState(account));
}
}
@Override
public void withdraw(double amount) {
System.out.println("Cannot withdraw, account is overdrawn! Current Balance: " + account.getBalance());
}
}
// BankAccount.java
public class BankAccount {
private double balance;
private AccountState state;
public BankAccount() {
this.balance = 0.0;
this.state = new NormalState(this);
}
public double getBalance() {
return balance;
}
public void setBalance(double balance) {
this.balance = balance;
}
public void setState(AccountState state) {
this.state = state;
}
public void deposit(double amount) {
state.deposit(amount);
}
public void withdraw(double amount) {
state.withdraw(amount);
}
}
// Client.java
public class Client {
public static void main(String[] args) {
BankAccount account = new BankAccount();
account.deposit(100);
account.withdraw(50);
account.withdraw(70); // This will trigger overdrawn state
account.deposit(30); // This will bring the account back to normal
account.withdraw(20);
}
}