Oops and enums

OOPS, ENUMS,
Inner Classes,
GarbageCollection
Satyam Shrivastav
http://programmingpoints.blogspot.in/
1

ASSOCIATION
 Association is a relationship between two objects.
 Objects might not be completely dependent on each
other.
 One-to-many, many-to-one, many-to-many all these
words define an association between objects
 Example: A Student and a Faculty are having an
association.
Satyam Shrivastav
2

AGGREGATION
 A directional association between objects.
 Aggregation can be considered as a “has-a”
relationship.
 Child object can also survive or exist without the
enclosing class.
 For Example, Room has a table, but the table can
exist without the room.
Satyam Shrivastav
3

COMPOSITION
 A restricted aggregation is called composition.
 The member object (part) cannot exist without the
containing class.
 For example, A class contains students. A student
cannot exist without a class. There exists composition
between class and students.
Satyam Shrivastav
4

UML Diagrams of
Relationships
 Association
Association is denoted by simple
arrow
 Aggregation
aggregation is denoted by empty
diamond head arrow
 Composition
composition is denoted by filled
diamond head arrow
Satyam Shrivastav
5

Difference Between
Composition And Aggregation
 When there is a composition between two objects, the
composed object cannot exist without the other object.
 In case of Aggregation,
Though one object can contain the other object,
there is no condition that the composed object must
exist.
 For Ex: Facebook has-a-User i.e. Aggregation
Every User has a different Session i.e.
Composition.
Satyam Shrivastav
6

METHODS OVERRIDING
 Overriding is a feature of OOP languages like
Java that is related to run-time polymorphism.
 Method overriding is when a child class
redefines the same method as a parent class,
with the same parameters.
 The key benefit of overriding is the ability to
define behavior that is specific to a particular
subclass type.
Satyam Shrivastav
7

The rules for overriding a method
are as follows:
 The argument list must exactly match that of the
overridden method.
 Overriding method CAN throw any unchecked
runtime exception.
 You cannot override a method marked final.
 You cannot override a method marked static.
 If a method can't be inherited, you cannot
override it.
Satyam Shrivastav
8

METHOD OVERLOADING
 Overloading is also a feature of OOP languages like
Java that is related to compile time (or static)
polymorphism.
 Method overloading is defining several methods in
the same class, that accept different numbers and
types of parameters.
 In this case, the actual method called is decided at
compile-time, based on the number and types of
arguments.
Satyam Shrivastav
9

Overloading Rules
 Overloaded methods MUST change the argument
list.
 Overloaded methods CAN change the return type.
 Overloaded methods CAN change the access
modifier.
 Overloaded methods CAN declare new or broader
checked exceptions.
 A method can be overloaded in the same class or
in a subclass.
Satyam Shrivastav
10

ENUM,
INNER CLASSES
Satyam Shrivastav
11

Enum
 An enumeration, or “enum” is simply a set of
constants to represent various values.
 An enum type is a special data type that enables for
a variable to be a set of predefined constants.
 The variable must be equal to one of the values that
have been predefined for it.
 enums extend java.lang.Enum and implement
java.lang.Comparable.
 Hence, enums can be sorted.
 Enums override toString() and provide valueOf().
Satyam Shrivastav
12

Defining Enum
 Old way of doing it:
public final int SPRING = 0;
public final int SUMMER = 1;
public final int FALL = 2;
public final int WINTER = 3;
 New way of doing it:
enum <enumname>{}
Satyam Shrivastav
13

Advantages
 Enums provide compile-time type safety.
 Enums provide a proper name space for the
enumerated type.
 Enums are robust.
 Enum printed values are informative
 Because enums are objects, you can put them in
collections.
 Because enums are classes, you can add fields and
methods.
Satyam Shrivastav
14

Inner Class
 The class defined inside another class or interface is
called inner class
 We can also create an interface in another class or
interface.
 For example
class Example{
class Sample{}
}
class Example{
interface Sample{}
}
interface Example{
class Sample{}
}
Satyam Shrivastav
15

Need of Inner Class
 Inner class is used for creating an object logically
inside another object with clear separation of
properties region.
 A inner class has access to the variables and methods
of the outer class, even if they are declared private.
 Nested classes can be hidden from other classes in
the same package.
Satyam Shrivastav
16

Nested class (static inner class)
 The inner class defined at class level with static
keyword is called static inner class.
 Syntax:
 Allowed Modifiers:
class Example{
static class A{}
}
private, protected, public, final, abstract, strictfp
 Types of Members allowed:
* static variable * non-static variable
* static block * non-static block
* static method * non-static method
* main method * constructor
Satyam Shrivastav
17

Inner class (non-static inner class)
 The inner class defined at class level without static
keyword is called non-static inner class.
 Syntax:
private, protected, public, final, abstract, strictfp
* non-static variable
* non-static block
* non-static method
* constructor
class Example{
class A{}
}
Satyam Shrivastav
18

Method Local class (local inner class)
 The inner class defined inside a method of outer
class called method inner class.
 Syntax:
final, abstract, strictfp
* non-static variable
* non-static block
* non-static method
* constructor
class A{
void m1(){
class B{}
}
}
Satyam Shrivastav
19

Anonymous class (argument inner class)
 It is a nameless subclass of some other existed
class/interface.
 Like other inner classes it is not individual class.
 Using anonymous class we can do 3 things at a time-
1. Inner class creation as a subclass of outer class.
2. Overriding outer class method.
3. Creating and sending its object as argument or
return type to another method.
Satyam Shrivastav
20

 Syntax:
new outerclassname(){
//overriding outer class methods
}
no modifier is allowed
* non-static variables
* non-static blocks
* non-static methods
Satyam Shrivastav
21

Cohesion,Coupling
And Garbage Collection
Satyam Shrivastav
22

Cohesion
Defintion:-
Cohesion means that a certain class performs a set of
closely related actions. Cohesion focuses on how
single class is designed.
Types of Cohesion:-
 High Cohesion
 Low Cohesion
Satyam Shrivastav
23

High cohesion:-
High cohesion is when you have a class that does a
well defined job.
Low cohesion:-
Low cohesion is when a class does a lot of jobs that
don't have much in common.
Higher the cohesiveness of the class, better is the OO
design.
Satyam Shrivastav
24

 Example:-
 You have a class that adds two numbers, but the
same class creates a window displaying the result.
 This is a low cohesive class because the window
and the adding operation don't have much in
common.
 The window is the visual part of the program and
the adding function is the logic behind it.
Satyam Shrivastav
25

What is Coupling?
Coupling:-
 Coupling is the degree to which one class knows
about another class.
 It refers to how related are two classes / modules
and how dependent they are on each other.
Types of Coupling:-
 Tight coupling
 Loose coupling
Satyam Shrivastav
26

Tight coupling:-
Tight coupling is when a group of classes are
highly dependent on one another.
Loose coupling:-
 Loose coupling would mean that changing
something major in one class should not affect the
other.
 Generally, good OO design should be loosely
coupled and highly cohesive.
Satyam Shrivastav
27

What is Garbage Collection ?
 Garbage collection is the process of identifying
which objects are in use and which are not, and
deleting the unused objects.
 In Java, process of deallocating memory is handled
automatically by the garbage collector.
 This enables faster development with less code,
eliminate memory leaks and other memory-related
problems.
Satyam Shrivastav
28

The ways to make an Object
eligible for GC:-
Even though the programmer is not responsible for
distruction of Object. It is a good programming
practice to make our object is eligible for the
Garbage Collection, if it is no longer required.
 Nullifying the reference variable :-
 Re-assigning the reference variable:-
 The Object created inside a method… are by
default eligible for GC.
Satyam Shrivastav
29

When the Garbage Collector Runs?
 The garbage collector is under the control of the JVM.
 The JVM will typically run the garbage collector when it
senses that memory is running low.
 User can request the JVM for garbage Collection
by Calling “System.gc()”.
 User can rely on ‘System.gc()’ to free up enough memory
without worrying for running out of memory.
 But the garbage collector will run before it throws an
OutOfMemoryException.
Satyam Shrivastav
30

Role of finalize() method in GC
 Java has a mechanism to run some code just before
your object is deleted by the garbage collector.
 This code is located in a method named finalize()
that all classes inherit from class Object.
 For any given object, finalize() will be called only
once (at most) by the garbage collector.
 Calling finalize() can actually result in saving an
object from deletion.
Satyam Shrivastav
31

“Thank You”
Satyam Shrivastav
32

Oops and enums

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