Software Construction: Object States

The state of an object refers to:

• the pieces of information the object represents at a given moment
• the actions that the object can perform at a given moment

State Space: Set of all possible states for an object.

Concrete State: Value(s) stored at a given moment.

Abstract State: Arbitrarily-defined subset of the state space.

The software design task of state space partitioning is to define abstract states that correspond to characteristics that will help construct a clean solution.

State diagrams allow us to self-evaluate the impact of design decisions on the complexity of the abstract state space that must be considered when working with an object.

Here the abstract state space would consist of State A & B.

Minimize the state space of objects to what is absolutely necessary for the object to fulfill its responsibilities.

Temporary FIeld is anti-pattern (don't do this!)

?? In this example the temporary value aSize is unnecessary, as the same information is in aCards.size ??

The state or property of being nullable.

I.e. if we don't want a reference to be null, we need to ensure this!

Java final variable: If you make any variable as final, you cannot change the value of final variable (It will be constant). A blank (null) final variable can only be initialized in the constructor!

Java final method: If you make any method as final, you cannot override it. A constructor can never be declared final (because it's never inherited)!

Java final class (object): If you make any class as final, you cannot extend it. Final fields do not make the referenced objects immutable! (i.e. only the reference pointer is immutable, but not the object itself)

The direct object reference is equal to it's pointer, not the object itself! If we want to compare 2 object by class / type we need to use ObjName.getClass()!