public class CheckingAccount extends BankAccount {
    private SavingsAccount overdraft;
    // Konstruktor:
    public CheckingAccount(int id, double initial, SavingsAccount savings) {
        super(id, initial);
        overdraft = savings;
    }
    // modifiziertes withdraw():
    public boolean withdraw(double amount) {
        if (!super.withdraw(amount)) {
            System.out.println("Using overdraft...");
            if (!overdraft.withdraw(amount-balance)) {
                System.out.println(
                    "Overdraft source insufficient.");
                return false;
            } else {
                balance = 0;
                System.out.println(
                    "New balance on account " 
                    + account + ": 0");
            } 
        }
        return true;
    }
} // end of class CheckingAccount