Java Design Pattern: Factory

1. The story for Factory pattern

Factory design pattern is used for creating an object based on different parameters. The example below is about creating human in a factory. If we ask the factory for a boy, the factory will produce a boy; if we ask for a girl, the factory will produce a girl. Based on different parameters, the factory produce different stuff.

2. Factory pattern class diagram

3. Factory pattern Java code

interface Human {
	public void Talk();
	public void Walk();
}
 
 
class Boy implements Human{
	@Override
	public void Talk() {
		System.out.println("Boy is talking...");		
	}
 
	@Override
	public void Walk() {
		System.out.println("Boy is walking...");
	}
}
 
class Girl implements Human{
 
	@Override
	public void Talk() {
		System.out.println("Girl is talking...");	
	}
 
	@Override
	public void Walk() {
		System.out.println("Girl is walking...");
	}
}
 
public class HumanFactory {
	public static Human createHuman(String m){
		Human p = null;
		if(m.equals("boy")){
			p = new Boy();
		}else if(m.equals("girl")){
			p = new Girl();
		}
 
		return p;
	}
}

4. Factory design pattern used in Java standard library

Based on different parameter, getInstance() returns a different instance of Calendar.

java.util.Calendar - getInstance()
java.util.Calendar - getInstance(TimeZone zone)
java.util.Calendar - getInstance(Locale aLocale)
java.util.Calendar - getInstance(TimeZone zone, Locale aLocale)
java.text.NumberFormat - getInstance()
java.text.NumberFormat - getInstance(Locale inLocale)

You can view the source code of Calendar and NumberFormat in javased.com.

Category >> Design Patterns Stories

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<pre><code> 
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</code></pre>

abc on 2013-10-24

The method is repeat
java_learner on 2013-10-29

good
eee on 2013-10-30

very good
Vetri on 2014-5-8

it s very good but this procedural approach is not a good idea in OOPS. if we have 10 or 20 classes implemented the Human interface . crateHuman(String) by String will be unreadable. so in a standard way you can use class registration with or without to avoid if else check in factory. since java reflection affects the performance by 10% . you can go with class registration without reflection .
for example.
Load all the classes before registering into factory using Class.forName() in order for this to work .

Class.forName(“Boy”);
Class.forName(“Girl”);

interface Human {
public void Talk();
public void Walk();
public Human createHuman();
}

class Boy implements Human {

static {
HumanFactory.getInstance().registerHuman(“boy”,new Boy());
}

@Override
public Human createHuman() {
return new Boy();
}

@Override
public void Talk() {
System.out.println(“Boy is talking…”);
}

@Override
public void Walk() {
System.out.println(“Boy is walking…”);
}
}

class Girl implements Human{

static {
HumanFactory.getInstance().registerHuman(“girl”,new Girl());
}

@Override
public Human createHuman() {
return new Girl();
}

@Override
public void Talk() {
System.out.println(“Girl is talking…”);
}

@Override
public void Walk() {
System.out.println(“Girl is walking…”);
}
}

public class HumanFactory {
private static HumanFactory humanfactory;
private Hashtable humanGroup = new Hashtable();

public static HumanFactory getInstance() {
if (humanfactory == null) {
synchronized(HumanFactory.class) {
if (humanfactory == null) {
humanfactory = new HumanFactory();
}
}
}
return humanfactory;
}

public void registerHuman(String name,Human human) {
humanGroup.put(name,Human);

}

public Human createHuman(String m){

Human human = (Human)humanGroup.get(m);
return human.createHuman();

/*Human p = null;
if(m == “boy”){
p = new Boy();
}else if(m == “girl”){
p = new Girl();
}

return p;*/
}
}
Vetri on 2014-5-8

typo mistake

class registration with or without reflection
Guest on 2014-6-17

Buen tutorial para este modelo de diseño! No pude encontrar algunos ejemplos como este (fácil y no confundir jaja) me voy a suscribirse a su boletín de noticias. Adiós y saludos desde Argentina!
Ezequiel Gustavo Martinez on 2014-6-17

Good tutorial for this design pattern! I couldn’t find out some examples like this (easy and not confused haha) I’ll subscribe me to your newsletter. Good bye and greetings from Argentina !
guest on 2014-6-23

Nice example, but when you compare String objects you should always use the equals method otherwise your factory object will always return null…
ryan on 2014-6-23

lol. Java people.
jeff on 2014-8-17

equals
malphix on 2014-9-28

method’s name lower….
Aayush Bahuguna on 2014-11-12

Nice example.

In HumanFactory for string comparison should m.equals(“boy”) / m.equals(“girl”) be used?
Curtis Newton on 2015-2-26

what about a more generic example, when you dont know the precise class
for instance if you got a list of classes that inherits a mother class ?
ryanlr on 2015-2-26

Glad to know the post is useful to you. Thanks for subscribing!
ryanlr on 2015-2-26

corrected. Thanks!
ryanlr on 2015-2-26

corrected, thanks!
ryanlr on 2015-2-26

I don’t understand your question, can you be more specific?
Anil Nivargi on 2015-7-21

Thanks for good explanation…..please go through this blog http://adnjavainterview.blogspot.in/2015/07/factory-design-pattern-in-java.html also explained good..

Java Design Pattern: Factory

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