Chapter 4: Objects and Classes

Chapter 4: Objects and Classes

1. Classes

   • Objects/Instance
     • Fields (Attributes)
       • int age; double salary; string position
       • references to objects
         • maxAge, validAddress,age
     • Methods (Actions or Functions)
       • work (); receiveSalary ()
       • define actions
       • declaration/signature of the method
         • consists of: return value, method name, and list of arguments
         • returnType methodName (listofArguments)
       • body
         • contains code that perform the action
       • return type: can be a primitive, an object, or void
         • void: nothing
       • accepts an argument:
         • int negate (int number)
       • does not accept arguments:
         • double getSalary ()
       • two or more arguments
         • int add (int a, int b)
       • main method
         • public static void main (String [ ] args)
         • java className arg1 arg2 arg3
     • creating objects:
       • new Employee () ;
       • Reference Variable
         • assign created object to a reference variable
           • Employee employee = new Employee () ;
             • employee is an object reference of type Employee
         • null keyword
           • when a reference variable does not have a value
           • Book book = null
     • objectReference.methodName
     • objectReference.fieldName
   • class Employee {
   • constructor
     • must have at least one
     • same name as class
     • no return value or void
     • constructorName (listofArguments) { [constructor body] }