How to implement Factory Design Pattern in Java ?.

Program to demonstrate how to implement Factory Design Pattern in Java.

1. Animal.java

package com.hubberspot.designpattern.creational.factorymethod;

// 1. Create a Animal interface
// having a method definition say eat
public interface Animal {

    public void eat();

}

2. AnimalFactory.java

package com.hubberspot.designpattern.creational.factorymethod;

// 2. Create a AnimalFactory which 
// will create instances of concrete
// Animals
public class AnimalFactory {

    // 3. Create a static getAnimal method which will
    // take package name + class name of class whose
    // instance is to be created.
    public static Animal getAnimal(String classInfo) {
        Animal animal = null;
        try {
            // 4. Class.forName(String) dynamically loads class
            // passed as a String to it. 
            // 5. newInstance() method creates a concrete instance of
            // the class passed to Class.forName() as a String.
            animal = (Animal) Class.forName(classInfo).newInstance();
        } catch (Exception e) {           
            e.printStackTrace();
        } 
        // 6. We return the concrete instance.
        return animal;
    }

}

3. Dog.java

package com.hubberspot.designpattern.creational.factorymethod;

// 8. Concrete animal Dog for the Animal interface
public class Dog implements Animal {

    @Override
    public void eat() {

        System.out.println("Dog eating .... ");

    }

}

4. Cat.java

package com.hubberspot.designpattern.creational.factorymethod;

// 7. Concrete animal Cat for the Animal interface
public class Cat implements Animal {

    @Override
    public void eat() {

        System.out.println("Cat eating .... ");

    }

}

5. TestFactoryDesignPattern.java

package com.hubberspot.designpattern.creational.factorymethod;

import com.hubberspot.designpattern.creational.factorymethod.Dog;

public class TestFactoryDesignPattern {

    public static void main(String[] args) {

        // 9. Create a Dog object from the AnimalFactory by passing fully
        // qualified name for the concrete Dog class
        Dog dog = (Dog) AnimalFactory.getAnimal(
                "com.hubberspot.designpattern.creational.factorymethod.Dog"
                );
        dog.eat();

        // 10. Create a Cat object from the AnimalFactory by passing fully
        // qualified name for the concrete Cat class
        Cat cat = (Cat) AnimalFactory.getAnimal(
                "com.hubberspot.designpattern.creational.factorymethod.Cat"
                );
        cat.eat();

    }


}

Output of the program :