Overview:

Before starting:

• Read over this entire document before you start.
• Read the CS101 Style Guide.
• If you need help, please ask.

Some particulars:

• The current value of a portfolio is its cash reserve plus the current market value of the shares of stock that are held.
• The current value of a single share of a particular stock can be obtained by

    Quote  Lab3.getStockQuote(String stockName)
  

  An API for Quote is given below.
• You will also find it useful to convert from a String that contains a numeral to the int number for the String. The following methods are provided in Lab3.java.

  • boolean Lab3.stringToIntOK(String)
    

    returns true if conversion can occur without error. Otherwise, false is returned.

  • int Lab3.stringToInt(String)
    

    returns the integer value of the supplied string. If the string has an error, then 0 is returned.
• In our system, money and stock worth are represented by MarketValue---an object type (class). We follow Wall Street in representing money by dollars and eighths of dollars.
• In the implementation, you will show the value of a portfolio in a SegmentDisplay window from Lab 2.

Portfolio

A portfolio contains

• a cash reserve
• some number of shares of one stock (Stock 1)
• some number of shares of another stock (Stock 2)
• the notion of a current stock -- the stock (Stock 1 or Stock 2) that is currently being bought or sold.

You must provide methods for the buying and selling of a portfolio's current stock. You must also provide a method that sets the current stock to Stock 1 or Stock 2.

Things to consider:

• What do the constructors look like?
• What instance variables are needed?
• How do you name your methods?
• What is the type signature for your methods that buy and sell stock? In particular,
  • Does one buy and sell stocks by specifying a number of shares, or an amount of money that should be spent on the transaction?
  • Can you allow for both?
• How do you represent the number and value of the shares of Stock 1 and Stock 2 that are held? For example, do you use ints or some class of your own design?

MarketValue

This class represents money in the form of dollars and eighths of dollars. For example

  MarketValue v1 = new MarketValue(3,4);

creates a value that is 3 dollars and 4/8 dollars, or $3.50. The toString method for MarketValue must print out the value in stock form: 3 4/8.

Although MarketValue may appear to be similar to Quote, you should view Quote as an interface for obtaining stock quotes, while MarketValue is much more general. In particular, think about methods you need to do the following.

• Let's say you have n shares of a stock, each with MarketValue v. What is the MarketValue of the n shares? Where does the method live that computes this? What is its type signature? Does it mutate to return the right value or does it create a new object to represent the value?
• You might think about having mutator and nonmutator methods that do similar things. For example, you might think of

    MarketValue plus(MarketValue addend)
  

  that returns a new MarketValue that represents the sum of this and the addend's MarketValue. You might also have

   void increase(MarketValue howmuch)
  

  that increments this MarketValue by howmuch.

What to turn in:

1. The cover sheet, properly completed
2. For each class in your design, including the Portfolio and MarketValue classes, provide the following.
   • A brief explanation of the intention and behavior of the class.
   • The API:
     • Instance Variables
     • Constructors
     • Accessors
     • Mutators
     • Other methods
   • Any useful invariants for the class. Recall in class that a bank account had the invariant

     balance >= 0
     

3. Be sure to do the same for any extra classes in your design.

• The names you use--they should be informative but not overly verbose.
• The style you use in spelling the names.
• The extent to which your methods will have unclear side-effects.
• The width of the methods' interface. For example, instead of passing a pair of values (such as dollars and eighths of dollars) around as separate parameters, you might invent an object to represent such pairs.

Quote API

Constructors

• Quote(String dollars, String eighths) constructs an immutable pair of Strings. Blanks are trimmed from the strings. If dollars or eighths is not positive, or not a number, then the associated instance variable is set to "0".
• Quote( ) constructs a Quote for 0 dollars and 0 eighths.
• Quote(String dollars) constructs a Quote for the specified dollars and 0 eighths.

Public Accessors

• String getDollars() returns the dollars.
• String getEighths() returns the eighths.

Other Public Methods

• String toString( ) returns a string with the dollars and eighths.

Public Fields

none

Private Methods

none

Private Fields

• dollars is the trimmed string containing dollars
• eighths is the trimmed string containing eighths

Invariants

• getDollars() returns a nonegative numeral
• getEighths() returns a nonnegative numeral whose value is less than 8.

Exceptional behavior

none