Factory Method Pattern

Factory Method Pattern:

• Problem: Using new keyword we can not create object with flexibility and by applying restrictions.
• Solution: Use Factory pattern (or) Factory method.
• By defining a abstract class or an interface but let the subclass  decide which class object to instantiate.
• A method of a class capable of constructing and returning its own class object or other class object is called "factory method".
• There are two types of factory methods.

1. Static factory method.
2. Instance factory method.

 1.Static Factory method:

• A static method defined to construct and return object of same class or different is known as static factory method.
• Some of the pre defined static factory methods are as follows.

1. Thread th= Thread.currentThread();
2. Class c=Class.forName();
3. Runtime rt=Runtime.getRuntime();
4. Calendar c=Calendar.getInstance();

2.Instance Factory method:

• A non static method defined to construct and return object of same class or different is known as instance factory method.
• Some of the pre defined instance factory methods are as follows.

1.  String s= new String("instance of");
    String s1=s.concat("java");
2. StringBuffer sb=new StringBuffer("instance of");
   sb=sb.subString(0,2);
3. Date d= new Date();
   String s=d.toString();

Program on Factory method / Factory Design pattern:

Step 1: create an interface:

1. package com.instanceofjavaforus;
2.  
3. public interface Vehicle {
4.  
5.  public void engine();
6.  
7. }
    

 Step 2: create a Two Wheeler class which implements vehicle interface:

1. package com.instanceofjavaforus;
2.  public class TwoWheeler implements Vehicle {
3.  
4.    @Override
5.     public void engine() {
6.         System.out.println("Two Wheeler");
7.     }
8.  
9. }

Step 3:: create a Four Wheeler class which implements vehicle interface:

1. package com.instanceofjavaforus;
2.  public class FourWheeler implements Vehicle {
3.  
4.    @Override
5.     public void engine() {
6.         System.out.println("FourWheeler");
7.     }
8.  
9. }

Step 4: create a SixWheeler class which implements vehicle interface:

1. package com.instanceofjavaforus;
2.  public class SixWheeler implements Vehicle {
3.  
4.    @Override
5.     public void engine() {
6.         System.out.println("SixWheeler");
7.     }
8.  
9. }

Step 5: create a TestEngine class which is having factory method:

1. package com.instanceofjavaforus;
2.  public class TestEngine {
3.  public Vehicle getVehicle(String venname){
4.      if(venname==null){
5.             return null;
6.        }else if(venname.equalsIgnoreCase("TwoWheeler")){
7.             return new TwoWheeler();
8.         }else if(venname.equalsIgnoreCase("FourWheeler")){
9.             return new FourWheeler();
10.         }else if(venname.equalsIgnoreCase("SixWheeler")){
11.             return new SixWheeler();
12.         }
13.     
14.         return null;
15.     }
16. }

Step 6: create a FactoryDemo class:

1. package com.instanceofjavaforus;
2.  public class FactoryDemo {
3.   public static void main(String args[]){
4.  
5.      TestEngine te= new TestEngine();
6.  
7.         Vehicle vehcle1=te.getVehicle("TwoWheeler");
8.        vehcle1.engine();
9.  
10.         Vehicle vehcle2=te.getVehicle("FourWheeler");
11.         vehcle2.engine();
12.  
13.         Vehicle vehcle3=te.getVehicle("SixWheeler");
14.          vehcle3.engine();
15.  }
16. }

1. OutPut:
2. TwoWheeler
3. FourWheeler
4. SixWheeler