Java™ Application Development on Linux - Dator

12.5 Finding the Methods and Attributes283remaining cards, we can quickly see that we have two cards that are accounts:“Capital Account” and “Current Account.” These are both pools of money.Put them on top of one another on the table. Likewise, it is fairly obvious that“CEO,” “CFO,” “Director,” and “Manager” are all people. Put them togetheron the table.Remember that we are looking for simplifying abstractions. The groupedcards should all be obviously variant types of a generic class of objects. In ourexample, the one is a stack of Accounts, and the other is a stack of People, or,as we will call them, Users. Create new cards for these generic classes. Make acard with “Account” at the top and put it above the first stack. Make anothercard with “User” at the top and put it above the second stack.There are two ways that this might simplify your design. For now, all cardsbelow the abstract cards are “on probation.” We are going to move on to definethe attributes (data) and methods (behavior) of our abstract classes. If the abstractclass can handle all use cases without having to treat any of the morespecific classes differently, then the specific cards are discarded. If not, then allfunctionality that is common across the more specific types will be put on theabstract class card, and only those data and behaviors that are different will beput on the more detailed cards.In the first case, the simplification is a reduction of several potential classesto a single class. This is always a good thing, when it is possible. In the secondcase, you are identifying potential inheritance relationships. 412.5FINDING THE METHODS AND ATTRIBUTESThe next step is to start identifying the data and behavior that characterize yourclasses. Always put such items on the most abstract class first. The only time toadd an attribute or method to a more specific class is when it applies to thatclass and only that class—in other words, only when it represents a differencebetween the general case and the specific case. 54. We’ll talk more about that later in the book. As it happens, all of our simplifications in thischapter are examples of the first case.5. In complex cases, you may find an attribute or method that applies to several, but not all,of the specific cases. In such a case, a new abstract class below the main abstract class, but aboveall the specific classes that share that attribute or method, may be called for.