Prototype Design Pattern in Java
Intent
Specify
the kinds of objects to create using a prototypical instance, and create new
objects by copying this prototype.
Motivation
When
we talk about object creation there is a better way to have new objects. If the
cost of creating a new object is large and creation is resource intensive, we
clone the object. Prototyping allows an object to create customized objects
without knowing their class or any details of how to create them. This pattern
involves implementing a prototype interface which tells to create a clone of
the current object.
The
best example to understand Prototype Patter is, the mitotic division of a cell
— resulting in two identical cells —that plays an active role in copying itself
and thus, demonstrates the Prototype pattern. When a cell splits, two cells of
identical genotype result. In other words, the cell clones itself.
Applicability
Use
the Prototype pattern when a system should be independent of how its products are
created, composed, and represented; and
·
When the classes to instantiate are
specified at run-time.
·
To avoid building a class hierarchy of
factories that parallels the class hierarchy of products.
·
When instances of a class can have one
of only a few different combinations of state.
Consequences
The
Prototype pattern has several benefits:
·
Adding and
removing products at run-time.
·
Specifying new
objects by varying values.
·
Specifying new
objects by varying structure.
·
Reduced
subclassing.
·
Configuring an
application with classes dynamically.
Implementation
|
import
java.util.ArrayList;
import
java.util.List;
public class Employees implements Cloneable{
private
List<String> empList;
public Employees(){
empList = new
ArrayList<String>();
}
public
Employees(List<String> list){
this.empList=list;
}
public void loadData(){
//This part
can be used to read data from the Database and add to List
empList.add("Ravi");
empList.add("Ajay");
empList.add("Sumit");
empList.add("Pooja");
}
public
List<String> getEmpList() {
return empList;
}
@Override
public Object
clone() throws CloneNotSupportedException{
List<String> temp = new
ArrayList<String>();
for(String s : this.getEmpList()){
temp.add(s);
}
return new Employees(temp);
}
}
|
|
import
java.util.List;
public class
TestPrototypePattern {
public static void main(String[]
args) throws
CloneNotSupportedException {
Employees emps = new Employees();
emps.loadData();
//Use the clone method to get
the Employee object
Employees empsNew = (Employees)
emps.clone();
Employees empsNew1 = (Employees)
emps.clone();
List<String> list = empsNew.getEmpList();
list.add("Simran");
List<String> list1 = empsNew1.getEmpList();
list1.remove("Sumit");
System.out.println("Existing
Employee List: "+emps.getEmpList());
System.out.println("Employee
List after adding an Employee : "+list);
System.out.println("Employee
List after removing an Employee : "+list1);
}
}
|
Output :
|
Existing Employee List: [Ravi, Ajay, Sumit, Pooja]
Employee List after adding an Employee : [Ravi,
Ajay, Sumit, Pooja, Simran]
Employee List after removing an Employee : [Ravi,
Ajay, Pooja]
|
