import java.math.*;

/** This class represents savings accounts. It implements state
    and behavior that define how a savings account differs from 
    a general bank account. */
public class SavingsAccount extends BankAccount { 
   /** Holds the string identifying the type of all savings accounts. */
   private static final String ACCOUNT_TYPE = "S";  
   /** Holds the interest rate "per period" paid on all savings accounts. */
   private static double interestRate;
   /** Return the interest rate. */
   public static double getInterestRate() { 
      return interestRate; 
   }  
   /** Set the interest rate. */
   public static void setInterestRate(double rate) { 
      interestRate = rate; 
   }  
   /** Create a new empty savings account. Note that the superclass
       constructor is also executed. */
   SavingsAccount() { }
   /** Return the account type string. */
  public String getAccountType() { 
      return ACCOUNT_TYPE; 
   }
   /** Return the maximum withdrawal amount. Withdrawals may be made only up to the
       current balance. */
   public BigDecimal getWithdrawalLimit() {
      return getBalance();
   }
   /** Post the interest for this period. Compute the interest amount and add it 
       to the current balance. */
   public void postInterest() {
      double interest = getBalance().doubleValue() * getInterestRate();
      setBalance(getBalance().add(new BigDecimal(interest)));
   } 
}