basic concepts on java

1. SEMINAR ON JAVA

2. INHERITANCE

3. THE MECHANISM
OF DERIVING A NEW
CLASS FROM AN OLD
ONE IS CALLED
INHERITANCE.

4. •THE OLD CLASS IS KNOWN
AS BASE CLASS OR SUPER
CLASS OR PARENT CLASS
THE NEW ONE IS CALLED
THE SUB CLASS OR DERIVED
CLASS OR CHILD CLASS

5. TYPES OF INHARITANCE

6. SINGLE INHERITANCE
•ONLY
ONE BASE
CLASS

7. MULTILEVEL
INHERITANCE
GRAND FATHER SUPER CLASS
FATHER INTERMEDIATE SUPERCLASS
CHILD SUB CLASS

8. A DERIVED CLASS WITH MULTILEVEL BASE CLASSES IS DECLARED AS
FOLLOWS
CLASS A
{
…………
…………
}
CLASS B extends A // first level
{
………….
………….
}
CLASS C //second level
{
………….
………….
}

10. EXAMPLE

11. HERE CERTAIN
FEATURES OF ONE
LEVEL ARE SHARED
BY MANY OTHER
BELOW THE LEVEL.

12. MULTIPLE INHERITANCE

13.  OVERRIDING CAN BE DONE BY
DEFINING A METHOD IN THE SUB
CLASS THAT HAS THE SAME
NAME,SAME ARGUMENTS AND
SAME RETURN TYPE AS A
METHOD IN THE SUPER CLASS.
 THIS IS KNOWN AS OVERRIDING.

14. FINALIZER METHODS
 FINILIZATION IS JUST OPPOSITE TO
INITIALASATION.
 JAVA RUN-TIME IS AN AUTOMATIC
GARBAGE COLLECTING SYSTEM.
 IT FREES THE MEMORY RESOURCES USED
BY OBJECTS.
 BUT OBJECTS MAY HOLD OTHER NON-
OBJECT RESOURCES SUCH AS FILE
DESCRIPTORS OR WINDOW SYSTEM
FONTS.

15.  THE GARBAGE COLLECTOR CANNOT FREE
THESE RESOURCES.
 IN ORDER TO FREE THIS WE USE FINALIZER
METHOD.
 THIS IS SIMILAR TO
DESTRUCTORS.
 THE FINALIZER METHOD IS SIMPLY
FINALIZE()

16. ABSTRACT METHODS
 FINALIZER
HELPS US NOT TO RE-
DEFINE THE METHOD IN SUB
CLASS.
 BUT
TO DO THE OPPOSITE, i.e.
REDEFINE THE METHOD IN SUB
CLASS,WE USE THE MODIFIER
KEYWORD abstract IN THE
METHOD DEFINITION

17. EXAMPLE
abstract class shape
{
………….
………….
abstract void draw();
………….
………….
}

18. VISIBILITY CONTROL
 IT
IS ALSO KNOWN AS ACCESS
MODIFIERS.THIS PROVIDES THREE
TYPES OF MODIFIERS:
PUBLIC
PRIVATE
PROTECTED

19. By simply declaring the variable or
method as public it is visible to
entire class in which it is defined.
A variable or method which is
declared as public has the widest
possible visibility and
accessible everywhere.

21. FRIENDLY ACCESS
• When no access modifier is specified,the
member defaults to a limited version of public
accessibility known as “friendly” level of
access.
• this makes fields visible only in the same
package,but not in other packages.

22.  The visibility lies in between the public
access and friendly access.
 The protected modifier makes the fields
visible not only to all classes and sub
classes in the same package but also to
sub classes in other packages.

23. PRIVATE ACCESS
 They enjoy the highest degree of protection.
 They are accessible only with their own class.
 They cannot be accessed and inherited
by sub classes.
 The method declared as private behaves like a
method declared as final.
 It prevents the method from being sub classed.

24. A field can be declared with two key
words private and protected together like:
Private protected int codenumber;
 the visibility level is between the
“protected” access and private access.
 This makes the fields visible in all
subclasses regardless of what package
they are in

25.  USE PUBLIC IF THE FIELD IS TO BE VISIBLE
EVERYWHERE.
 USE PROTECTED IF THE FIELD IS TO BE
VISIBLE EVERYWHERE IN THE CURRENT
PACKAGE AND ALSO SUBCLASSES IN
OTHER PACKAGES.
 USE “DEFAULT” IF THE FIELD IS TO BE
VISIBLE EVERYWHERE IN THE CURRENT
PACKAGE ONLY.
 USE PRIVATE PROTECTED IF THE FIELD IS

27. thank you