Object Life Cycle
One way of thinking of objects is that they have a life cycle. All of
these things happen in a file outside the object’s class. The class is merely
code that the object will use.
|
Event |
Description |
Example |
|
Declaration |
Planning which type of object you will have. |
Button exit; |
|
Construction |
Getting the instance variables and memory ready to use. |
Exit = new Button (“Hi”); |
|
Accessors/ Inspectors |
Return the values of the instance variables. Generally named get--- |
A = exit.getLabel(); |
|
Mutators |
Changes or mutates the values of the instance variables. Generally named set--- |
Exit.setLabel(“Yippee”); |
|
Facilitators |
Does something useful. These are generally the most difficult methods
to code. |
Button doesn’t really have any. CompareTo is a pretty good example
of one. If (exit.getLabel().compareTo (“Turkey”)==0) … |
|
Destructors |
Clean up memory when the object is not longer used. |
You don’t need to code this in Java, the compiler does it for you!! |
Here is an analogy to help you remember the object life cycle. The first
one is building a house. The declaration occurs when the builders make the
blueprints. The constructor occurs when the house is being built. A mutator is
sort of like a family moving into a house. The family living in the house can
change. A facilitator is things that the house can do: have its grass mowed, get
new paint, have mailed delivered, build a garage. A accessor is information
about the house which is made available – say the address painted by the front
door. The house is destroyed when
the bulldozers come in to make way for a new subdivision.
Questions