我正在尝试在一个简单的银行系统上实现和‘撤销’JButton，它将撤销上一次执行的操作

import java.util.Stack;

public class BankSystem {
    private double balance;
    private Stack<Operation> history;

    public BankSystem() {
        balance = 0.0;
        history = new Stack<>();
    }

    public void deposit(double amount) {
        balance += amount;
        history.push(new Operation(OperationType.DEPOSIT, amount));
    }

    public void withdraw(double amount) {
        if (balance >= amount) {
            balance -= amount;
            history.push(new Operation(OperationType.WITHDRAW, amount));
        } else {
            System.out.println("Insufficient balance.");
        }
    }

    public void undo() {
        if (!history.isEmpty()) {
            Operation lastOperation = history.pop();
            if (lastOperation.getType() == OperationType.DEPOSIT) {
                balance -= lastOperation.getAmount();
            } else if (lastOperation.getType() == OperationType.WITHDRAW) {
                balance += lastOperation.getAmount();
            }
        } else {
            System.out.println("No operations to undo.");
        }
    }

    public double getBalance() {
        return balance;
    }

    public static void main(String[] args) {
        BankSystem bank = new BankSystem();
        bank.deposit(100.0);
        System.out.println("Balance: " + bank.getBalance());
        bank.withdraw(50.0);
        System.out.println("Balance: " + bank.getBalance());
        bank.undo();
        System.out.println("Balance: " + bank.getBalance());
    }
}

enum OperationType {
    DEPOSIT,
    WITHDRAW
}

class Operation {
    private OperationType type;
    private double amount;

    public Operation(OperationType type, double amount) {
        this.type = type;
        this.amount = amount;
    }

    public OperationType getType() {
        return type;
    }

    public double getAmount() {
        return amount;
    }
}