Mapa mental

Heuristics

Annie Chase Español

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Heuristics

Find Real-World Objects
- Identifying real-world and synthetic objects
  - Steps
    - Identify methods and data
      - What can be done to an object?
        What each object is allowed to do to others?
        Which parts will be public and which will be private?
        Define each object’s public interface
        Programming-language
        Formal
        Syntactic
        Operations can be performed on an object
      - Relevant characteristics
Form Consistent Abstractions
- Abstraction
  - Handle different details at different levels
    - Example
      - A good class interface is an abstraction that allows you to focus on the interface without needing to worry about the internal workings of the class
  - Simple view, complex concept
Encapsulate Implementation Details
- Manage complexity by forbidding you to look at the complexity
  - Basically
    - What you see is what you get—it’s all you get!
Inherit
- Defining similarities and differences among objects
  - Different levels of details
- Benefit
  - Works with abstraction
Hide secrets/Information hiding
- Foundation
  - Structured design
    - Black boxes
  - Object-oriented design
    - Encapsulation
    - Modularity
    - Abstraction
- Good class interface
  - Leaves most of it unexposed
Identify Areas Likely to Change
- Isolate unstable areas
  - Steps
    - Identify items that seem likely to change
      - Separate items that are likely to change.
        Isolate items that seem likely to change
        Interclass interfaces are insensitive to potential changes
        Compartmentalize volatile components
- Some areas
  - Business rules
  - Hardware dependencies
  - Input and output
  - Nonstandard language features
  - Difficult design and construction areas
  - Status variables
Keep Coupling Loose
- Coupling
  - How tightly a class or routine is related to others
  - Coupling criteria
    - Size
    - Visibility
    - Flexibility
  - Kinds of coupling
    - Simple-data-parameter
      - All the data passed between them are of primitive data types and all the data is passed through parameter lists
    - Simple-object
      - A module instantiates an object
    - Object-parameter
      - Object1 requires Object2 to pass it an Object3
    - Semantic coupling
      - Module makes use of some semantic knowledge of another module’s inner workings
- Goal
  - Create classes with small relations
Look for Common Design Patterns
- Provide the cores of ready-made solutions
- Pattern
  - Provide several benefits that fully custom design doesn’t
  - Reduce complexity
    - Provide ready-made abstractions
  - Reduce errors
    - Institutionalizing details of common solutions
  - Provide heuristic value
    - Suggests design alternatives
  - Streamline communication
    - Moving the design dialog to a higher level
  - Popular Design Patterns
    - Abstract Factory
    - Adapter
    - Bridge
    - Composite
    - Decorator
    - Facade
    - Factory Method
    - Iterator
    - Observer
    - Singleton
    - Strategy
    - Template Method
Other Heuristics
- Aim for Strong Cohesion
  - Cohesion
    - How focused the class is
    - Useful tool for managing complexity
      - More that code in a class supports a central purpose
        Easier for your brain to remember everything
- Build Hierarchies
  - Hierarchy
    - Tiered information structure
      - Most general representation of concepts is at the top
        Specialized representations at the lower levels
    - Allow to focus on only the level of detail currently concerned with
- Formalize Class Contracts
  - Class interface is a contract with the rest of the program
    - Useful for managing complexity
      - Object can safely ignore any noncontractual behaviour
- Assign Responsibilities
  - How responsibilities should be assigned to objects
- Design for Test
  - Ask what the system will look like if you design it to facilitate testing
    - Result in
      - More formalized class interfaces
- Avoid Failure
- Choose Binding Time Consciously
  - Binding time
    - Time a specific value is bound to a variabe
      - Code that binds early tends to be simpler
        Tends to be less flexible
- Make Central Points of Control
  - Control
    - Centralized in
      - Classes
      - Routines
      - Preprocessor macros
  - Fewer places to look for something
- Consider Using Brute Force
  - Better than an elegant solution that doesn’t work
- Draw a Diagram
  - Can represent the problem at a higher level of abstraction
- Keep Your Design Modular
  - Modularity
    - Goal
      - Black box
    - Related to
      - Encapsulation
      - Information hiding