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Factory
Method:
Definition:
A
factory method is one whose return type is similar to class name in which class
name it
presents.
The purpose of Factory method to create an object
without using new operator.
Rules for
developing Factory Method:
1) The return
type of the factory method must be always similar to name of the class. In
which class it presents.
2) The nature
of factory method must be always static.
3) Access
Specifier of factory method be Public.
For
Example:
Real Time
Example in JDK API
1) GraphicsEnvironment
Public static
GraphicsEnvironment
Rule 3 Rule 2 Rule1
getLocalGraphicsEnvironment
Method
From above example we can
understand that under GrapshicsEnvironment class
getLocalGraphicsEnvironment
method return type is class name (i.e: GraphicsEvironment)
of nature static.
2) String
Public
static String valueOf(Xxx)
Rule 3 Rule 2 Rule1
Method
3) Class
Public
static Class
Rule 3 Rule 2 Rule1
forName(String) throw
ClassNotFoundException
Method
The Following Example illustrate the
concept of Factory Method:
//The
Following User defined Example for Factory Method.
// FMDemo.java
public Class FMDemo{
public static FMDemo fun1(){
FMDemo fmd=new FMDemo();
Return fmd;
}
}
What are different types
of factory method s in java ?
There are two types of
factory methods in java. They are
1) Static
factory method.
2) Instance
factory method.
Static
Factory Method:
Factory method produces an object and produced
object may be of same class or may be different class.
In real scenarios we observe can Calendar, thread
, InetAddress, Class …..etc
classes are comes under static Factory methods
Examples of static factory methods:
a) Class
c=Class.forName(“java.lang.String”):
b) Calendar
c=Calendar.getInstance();
c) Thread
t=Thread.CurrentThread();
Instance Factory Method:
Instance factory method in java we can create instance factory methods also
generally
factory methods also generally we use instance factory methods to
produce one class
object from another class.
For Example:
Public class A{
----------// Block
of statements
----------
}
Public class B{
Public A
getInstance() {
return
new A();
}
}
getInstance method is
producing an object of class A and it is instance method not a static
method.
So this getInstance method is called Instance Factory method.
Advantages:
1.
Static factory methods is that, not like
constructors, they have names.
2.
Static factory methods is that, not like
constructors, they are not required to create a new object each time they’re
invoked.
3.
Static factory methods is that, not like
constructors, they can return an object of any sub type of their return type.
4.
Static factory methods is that they reduce the
verbosity of creating parameterized type instances.
Disadvantages:
1.
Only static factory
methods is that classes without public or protected constructors cannot into sub
class.
2.
static factory methods is that they are not
readily to differ from other static methods.
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