Creational Patterns - Factory Pattern

Factory of what? Of classes. In simple words, if we have a super class and n sub-classes, and based on data provided, we have to return the object of one of the sub-classes, we use a factory pattern.

Let’s take an example to understand this pattern.

Example: Let’s suppose an application asks for entering the name and sex of a person. If the sex is Male (M), it displays welcome message saying Hello Mr. <Name> and if the sex is Female (F), it displays message saying Hello Ms <Name>.

The skeleton of the code can be given here.

public class Person {
	// name string public String name; // gender : M or F private String gender; public String getName() { return name; } public String getGender() { return gender; }
}// End of class

This is a simple class Person having methods for name and gender. Now, we will have two sub-classes, Male and Female which will print the welcome message on the screen.

public class Male extends Person {
	public Male(String fullName) { System.out.println("Hello Mr. "+fullName); }
}// End of class

 

Also, the class Female

public class Female extends Person {
	public Female(String fullNname) { System.out.println("Hello Ms. "+fullNname); }
}// End of class

Now, we have to create a client, or a SalutationFactory which will return the welcome message depending on the data provided.

public class SalutationFactory {
	public static void main(String args[]) { SalutationFactory factory = new SalutationFactory(); factory.getPerson(args[0], args[1]); } public Person getPerson(String name, String gender) { if (gender.equals("M")) return new Male(name); else if(gender.equals("F")) return new Female(name); else return null; }
}// End of class

This class accepts two arguments from the system at runtime and prints the names.

Running the program:

After compiling and running the code on my computer with the arguments Prashant and M:

java Prashant M

The result returned is: “Hello Mr. Prashant”.

When to use a Factory Pattern?
The Factory patterns can be used in following cases:
1. When a class does not know which class of objects it must create.
2. A class specifies its sub-classes to specify which objects to create.
3. In programmer’s language (very raw form), you can use factory pattern where you have to create an object of any one of sub-classes depending on the data provided.