• Class:
  • A definition of a set that is written in terms of the characteristics of the elements (rather than by listing the elements)
• Characteristics (a.k.a., Members):
  • Both attributes and behaviors
• Encapsulation:
  • (v) The process of defining an entity in terms of its characteristics
  • (n) A result of the encapsulation process

access class class-name
{

• Getting Started:
  • Students are only expected to go from a textual description of a class to a final encapsulation (using a refinement process)
• By the End:
  • Students are expected to understand and use several software processes to go from needs and desires to deployment

• Attributes/Fields:
  • Identify the noun phrases in the description
  • Think about the data types to use for each noun phrase
• Behaviors/Methods:
  • Identify the verb phrases in the description
  • Think about the parameters for each verb phrase

• An Observation:
  • A method will probably need to use some or all of the attributes but may also need to use other values that are not part of the definition of the class
• An Obvious Solution:
  • Use variables (in addition to the attributes)

• Local Variables:
  • Have subprogram scope
  • Can only be used in the method that declares them
• Attributes:
  • Can be used in all methods in the class
  • this can be used to disambiguate between local variables/formal parameters and attributes with the same name

• How We Described it Earlier:
  • It's used to disambiguate attributes and local variables/parameters that have the same name
• An Observation:
  • It is used as the left-side operand of the . operator (i.e., the membership operator) so must refer to an object
• Internally:
  • A reference of the calling object

• Purpose:
  • Constructors perform initializations required when an object is created
• Syntax:
  • A constructor has no return type and the same name as the class
• Use:
  • A constructor is called indirectly using the new operator

1. Read the textual description
2. Create an initial encapsulation
3. Add a constructor

A picture frame is used to display a picture. It always has a width and height (measured in inches). It may or may not have a matte/border (also measured in inches). If it has a matte, it is the same size on all four sides. One can calculate the visible area of a picture frame from its area and the area of the matte.

A picture frame may or may not have a stand.

One can calculate the cost of a picture frame from the amount of material used in the perimeter of the frame itself and the area of the glass.

A picture frame is used to display a picture. It always has a width and height (measured in inches). It may or may not have a matte/border (also measured in inches). If it has a matte, it is the same size on all four sides. One can calculate the visible area of a picture frame from its area and the area of the matte.

A picture frame may or may not have a stand.

One can calculate the cost of a picture frame from the amount of material used in the perimeter of the frame itself and the area of the glass.

A picture frame is used to display a picture. It always has a width and height (measured in inches). It may or may not have a matte/border (also measured in inches). If it has a matte, it is the same size on all four sides. One can calculate the visible area of a picture frame from its area and the area of the matte.

A picture frame may or may not have a stand.

One can calculate the cost of a picture frame from the amount of material used in the perimeter of the frame itself and the area of the glass.

• An Observation:
  • When debugging, we often want to see all of an object's attributes
• The Implication:
  • Always include a method (commonly named toString() that returns a human-readable String representation of all of the (important) attributes

1. Read the textual description
2. Create an initial encapsulation
3. Add a constructor
4. Add a toString() method

• An Observation:
  • We often want to compare the attributes of two objects (of the same class)
• The Implication:
  • Always include an equals() method that returns true if the attributes are the same
  • Include a compareTo() method of objects can be ordered

1. Read the textual description
2. Create an initial encapsulation
3. Add a constructor
4. Add a toString() method
5. Add an equals() method