Java Lecture Notes - 2012.02.20

example)
public class PrintlnMethod {
    public static void main( String[] args ) {
    // println()using print different values
    System.out.println( 3 );
    System.out.println( 3.14 );
    System.out.println( 'c' );
    System.out.println( "gemini" ); 
    // System : class / out : staticmember
 }
}

data type
   1) primitive type : value pass call by value
         int a=5;
         float f=4.5;

         …..

         methodA(a,f);                // methodA actual parameter   call : call by value

         methodA(int b, float g) {    // methodA formal parameter call : call by value

         ……..

         }

   2) composite type : address  "   call by reference :object startaddress value pass

         class A {

          int a;

          int b; 

         }

         ……

         A obA = new A(); ………

         methodA(obA) // methodA call

 



 

inheritance

     JDKfrom top-level class = object class (rt.jar>java.lang>object class)

     (object class->) A class-> B class
           inheritance O : memberfunction,datamember

           inheritance X : creation,private
 

      object class : address type = object  definition
      A class :        address type = object , A class definition
      B class :        address type = object , A class, B class definition

           object auto type conversion (addresstype therefore addressvalues substitute can.)

            subclasstype contained in object address 

            parentclasstype's reference variable address value substitute can.

            o : A class -> object class

            o : B class -> A class

           address value substitute (forced type conversion) => cast operator utilize 

            x : object class -> A class

           x : A class -> B class

polymorphism implementation
      overloading(overloading) : duplicatefunction

            same class within same name constructor or method(memberfunction) using behavior

            parametervariable count and type must differ !

            parametervariable count and type occurrence form executioncondition auto passed.

            however,parametervariable typeonly case X !

      over(overriding) : re-definition

            inheritancerelationship class

            function header must occurrencemust .

            parametervariable count and type same .

            O = private -> default (omitted's case) -> protected -> public

            x = public -> protected -> default (omitted's case) -> private

 

 
example) 

     Object  : public void String toString(){ //function re-definition

          AA   : public void String toString(){}

          BB   : public void String toString(){}

          CC   : public void String toString(){}

     }
     //public change.