UML

• private field 2 : String

protected field : Integer |

| - private method (Args) : ReturnType

• public method () : String
• public abstract method () : Integer |

IS-A (Inheritance): Arrow from a box to the base class.

OWNS-A (Ownership): Black diamond from the owning class with an arrow to the owned class.

• If A owns B, then when A is destroyed, so is B.
• B does not have an independent existence. B exists for the sole purpose of A.
• Example: Car OWNS-A Motor. When a car is destroyed, so is the motor. RAII is also a good example of following OWNS-A.

HAS-A (Shallow Membership): Arrow is same as OWNS-A, but the diamond is white.

• If A has B, then when A is destroyed, nothing happens to class B.
• B is an independent existence.
• Example: Pond HAS-A Duck. When a pond is destroyed, the ducks are still alive. They just fly away.

SOLID

Single Responsibility Principle: A class should only have one reason to change.

Open-Closed Principle: Classes, modules, functions, etc. should be open for extension but closed for modification.

Coupling and Cohesion

We want low coupling, high cohesion.

Coupling: Strength of interdependence of modules.

• Low: Modules interact with each other simply; X doesn't rely on Y's internal implementation
• High: Implementation of X changes if Y changes

Cohesion: Closeness of relations between modules.

• Low: Arbitrary grouping (<utility> library)
• High: Modules cooperate to complete one exact task