Recap: Objects and Names

1
Recap Objects and Names

• There are two types of things in Java
• Objects
• the button that the user just pressed
• the URL of your home page
• Primitive-type things
• The integer that represents the number of times
  you have visited Alaska
• The character that represents your middle initial
• There are 8 primitive types, all of which begin
  with a lower-case letter
• The most commonly used are int, double, char and
  boolean
• Less common are long, short, byte and float
• We use names (also called variables) to refer to
  objects
• buttonUserPressed homeURL mobyDick
• and to primitive-type things
• numberOfTimesVisitedAlaska
• middleInitial

2
What can you do with names?

• Java is a strongly typed language every name
  must have a type. The type of an object helps
  the compiler
• (and programmer) tell what kinds of thing the
  object can do
• write more efficient code

The type name pattern appears often in Java

• Declare the type of the name
• JButton buttonUserPressed
• char middleInitial
• Give (assign) a value to the thing to which the
  name refers
• buttonUserPressed new JButton(press me)
• yourMiddleInitial C
• Refer to the thing to which the name refers, in
  an expression
• buttonUserPressed.isEnabled()
• numberOfTimesVisitedAlaska
• System.out.println(yourMiddleInitial)

These dot notation references are where the power
of an OOP language lies!
3
Object-type versus primitive-type

• An object-type name is justa label stuck onto an
  object.
• Objects are always given label names.
• Dog familyDog myPet
• A primitive-type name is like a dial it refers
  to its value, rather than merely being a label
  stuck onto that value
• Primitive types (int, double, char, boolean and a
  few others) always have primitive-type names
  associated with them.
• int count 9 char grade
• boolean isSleepy true

Questions?