Lecture 16 – March 12, 2007

Lecture 15 – March 13, 2007

First example of extending a class

GradedActivity2.java

FinalExam2.java

Let’s look at the copy constructor example in the text (found on page 569)

What we are interested in, in this example, is just the mechanism for creating a copy constructor.

Stock.java

CopyConDemo.java

Now, let me point out that the copy constructor example in the book is not a good one because two companies can’t have the same trading symbol.

Note that, copy constructors are very useful when you want to have different (separate objects) with the same attributes.

An example might be a poker hand where

each player has an initially empty array of 5 cards

each player has an initially empty string representing the type of hand

Another example might be a hash table where you want to create a copy of the table to play with not the real table.

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We have said that we want all declarations of variables at the top of methods.

When you try to do this in a constructor you get an error message if the constructor calls its super class constructor.
This is because you’re trying to muck with the object before it has been created.
This is the one place where it is not only OK but required that you declare the variable AFTER other code in a method.

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What about the over ridden method getAccountNumber?

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Professor Harris is helping students with major applications. Please be sure to see her as soon as possible.

There is an ACM sponsored event tomorrow evening Consulting 101 with food. You do not have to be an ACM member to attend. You should have gotten an e-mail message about it and if you deleted it, the time and place are posted on the bulletin board outside my office.

Below are the two methods you were asked to write for Lab 15 which we discussed in class

/**
    @author Elizabeth Adams
March 13, 2007 - for Lab 15 from Gaddis
Note that the commented out statements were discussed in class/
Some of them show alternate ways of coding a method.
Others show things that didn't quite match specifications

*/
public class CheckingAccount extends BankAccount
{
//    public final double FEE = .15;
   private static final double FEE = 0.15 ;

public CheckingAccount(String name , double initAmount )
{
   // String temp;
    super(name, initAmount);
  String temp;
    temp = getAccountNumber();
    temp = temp + "-10";
    setAccountNumber(temp);
// setAccountNumber ( getAccountNumber() + "-10");

}// end constructor

// super class withdraw header shown - method was to be over ridden

    // public boolean withdraw(double amount)
public boolean withdraw (double amount)
{
    boolean result;
    amount = amount + FEE;
   result = super.withdraw(amount);
   return result;
   // return (super.withdraw(amount));

}// end withdraw
}// end class

/**
@author Elizabeth Adams
March 13, 2007
Written for Lab15 based on instructions in Gaddis
Commented statements were discussed in class
This version doesn't use the required over ridden method
getAccountNumber()
*/
public class SavingsAccount extends BankAccount
{
private double rate; //= 0.025;
   private int savingsNumber; // = 0;
   private String accountNumber;

public SavingsAccount (String name, double initBalance)
  {
     super (name, initBalance);
     String temp; // has to be declared AFTER call to super
    rate = 0.025;
    savingsNumber = 0;
     temp = super.getAccountNumber();
     accountNumber = temp + "-" + savingsNumber;
}// end constructor

// copy constructor described on page 569 of text_
public SavingsAccount (SavingsAccount oldSavingsAccountObject,

                        double initBalance)
{
   super(oldSavingsAccountObject, initBalance);
String temp;
savingsNumber = oldSavingsAccountObject.savingsNumber + 1;
   temp = super.getAccountNumber();
   accountNumber = temp + "-" + savingsNumber;
}// end copyconstructor

public void postInterest ()
{
      // calculates one month's worth of interest on the balance
     _// and deposits it into the account
   double tempBalance;
   tempBalance = getBalance();
   tempBalance = tempBalance + tempBalance * (1.0/12.0) * rate;
   setBalance(tempBalance);
}// end postInterest

   /**accessor method to account number
      @return the account number*/
       public String getAccountNumber()
      {
          return accountNumber;
      } // end overRidden getAccountNumber;
}// end class

Here are links to the other code discussed in class. They point to Word files.