Ch. 4 Objects and Classes

Ch. 4 Objects and Classes

1. What is a Java Object?

   • OOP can be used to show and solve real-life situations
   • Java objects have attributes and actions called fields and method, respectively
     • Fields and methods are optional
   • Classes are used to create Java objects

2. Java Classes

   • Class determines the object
   • Consider 3 things when writing a class
     • Class name
     • The fields
     • The methods

3. Fields

   • variables that can reference to objects
   • Follow camel naming convetion
     • ie. maxAge

4. Methods

   • define what objects can do
   • Has declaration and body part
     • Declaration part
       • Return value
         • can be a primitive (field)
         • can be object
         • can be void
       • method name
       • list of arguments
     • body part
       • code that performs action

5. Method "main"

   • Provides entry to application
   • allows class containing to be invoked

6. Constructors

   • Every class needs at least 1 constructor
     • compiler adds 1 if not specified
   • no return value

7. Creating Objects

   • use "new"
   • usually create reference variable

8. null Keyword

   • no return value
   • Test if reference variable is null with "==" operator