public class CheckingAccount {
   private double balance;
   private int number;
   public CheckingAccount(int number) {
      this.number = number;
   }
   public void deposit(double amount) {
      balance += amount;
   }
   public void withdraw(double amount) throws InsufficientFundsException {
      if(amount <= balance) {
         balance -= amount;
      }else {
         double needs = amount - balance;
         throw new InsufficientFundsException(needs);
      }
   }
   public double getBalance() {
      return balance;
   }
   public int getNumber() {
      return number;
   }
    @Override
    public String toString() {
        return "Account number: " + number + ", Balance: " + balance;
    }
}