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SUBSCRIBE NOWUnderstanding the Builder Design Pattern
The Builder Design Pattern is a creational design pattern that allows you to construct complex objects step by step. When building complex domain models—such as customizable animal toys with distinct heads, bodies, legs, and colors—relying on massive constructors (the telescoping constructor anti-pattern) makes code difficult to read, maintain, and test.
By separating the construction process from the actual product representation, the Builder pattern enables the exact same construction sequence to create different variations of a complex object.
Complete Java Code Walkthrough
Here is an end-to-end, clean implementation demonstrating how to build animal toys step-by-step using the Builder design pattern in Java:
// 1. Product Class
class AnimalToy {
private String head;
private String body;
private String legs;
private String sound;
public void setHead(String head) { this.head = head; }
public void setBody(String body) { this.body = body; }
public void setLegs(String legs) { this.legs = legs; }
public void setSound(String sound) { this.sound = sound; }
@Override
public String toString() {
return "AnimalToy [head=" + head + ", body=" + body + ", legs=" + legs + ", sound=" + sound + "]";
}
}
// 2. Builder Interface
interface AnimalToyBuilder {
void buildHead();
void buildBody();
void buildLegs();
void buildSound();
AnimalToy getToy();
}
// 3. Concrete Builder: Lion Toy
class LionToyBuilder implements AnimalToyBuilder {
private AnimalToy toy = new AnimalToy();
@Override
public void buildHead() { toy.setHead("Lion Mane Head"); }
@Override
public void buildBody() { toy.setBody("Golden Fur Body"); }
@Override
public void buildLegs() { toy.setLegs("4 Strong Paws"); }
@Override
public void buildSound() { toy.setSound("Roar!"); }
@Override
public AnimalToy getToy() { return this.toy; }
}
// 4. Concrete Builder: Elephant Toy
class ElephantToyBuilder implements AnimalToyBuilder {
private AnimalToy toy = new AnimalToy();
@Override
public void buildHead() { toy.setHead("Elephant Trunk & Ears Head"); }
@Override
public void buildBody() { toy.setBody("Grey Tough Body"); }
@Override
public void buildLegs() { toy.setLegs("4 Pillar Legs"); }
@Override
public void buildSound() { toy.setSound("Trumpet!"); }
@Override
public AnimalToy getToy() { return this.toy; }
}
// 5. Director Class
class ToyCreator {
private AnimalToyBuilder builder;
public ToyCreator(AnimalToyBuilder builder) {
this.builder = builder;
}
public void assembleToy() {
builder.buildHead();
builder.buildBody();
builder.buildLegs();
builder.buildSound();
}
public AnimalToy getToy() {
return builder.getToy();
}
}
// 6. Client Application
public class AnimalToyDemo {
public static void main(String[] args) {
// Build a Lion Toy
AnimalToyBuilder lionBuilder = new LionToyBuilder();
ToyCreator lionCreator = new ToyCreator(lionBuilder);
lionCreator.assembleToy();
AnimalToy lionToy = lionCreator.getToy();
System.out.println("Created: " + lionToy);
// Build an Elephant Toy
AnimalToyBuilder elephantBuilder = new ElephantToyBuilder();
ToyCreator elephantCreator = new ToyCreator(elephantBuilder);
elephantCreator.assembleToy();
AnimalToy elephantToy = elephantCreator.getToy();
System.out.println("Created: " + elephantToy);
}
}Key Architectural Advantages
- Step-by-Step Construction: Breaks down complex assembly pipelines into discrete, readable, and manageable methods.
- Single Responsibility Principle: Isolates complex construction logic from the domain representation (
AnimalToy). - Reusability with Director: The
ToyCreatorcontrols the execution sequence, allowing different builders to generate completely different products using the exact same assembly process.
Watch More Related Design Pattern Tutorials
Click here to watch in Youtube : https://www.youtube.com/watch?v=zgPpKTUYux8
Click the below Image to Enlarge
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| Builder Design pattern - Implementation [Animal Toy] |
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| Builder Design pattern - Implementation [Animal Toy] - Class Diagram |
AnimalToy.java
public class AnimalToy
{
private String animalToyName;
private String animalToyHead;
private String animalToyBody;
private String animalToyArms;
private String animalToyLegs;
private String animalToyTail;
public String getAnimalToyName()
{
return animalToyName;
}
public void setAnimalToyName( String animalToyName )
{
this.animalToyName = animalToyName;
}
public String getAnimalToyHead()
{
return animalToyHead;
}
public void setAnimalToyHead( String animalToyHead )
{
this.animalToyHead = animalToyHead;
}
public String getAnimalToyBody()
{
return animalToyBody;
}
public void setAnimalToyBody( String animalToyBody )
{
this.animalToyBody = animalToyBody;
}
public String getAnimalToyArms()
{
return animalToyArms;
}
public void setAnimalToyArms( String animalToyArms )
{
this.animalToyArms = animalToyArms;
}
public String getAnimalToyLegs()
{
return animalToyLegs;
}
public void setAnimalToyLegs( String animalToyLegs )
{
this.animalToyLegs = animalToyLegs;
}
public String getAnimalToyTail()
{
return animalToyTail;
}
public void setAnimalToyTail( String animalToyTail )
{
this.animalToyTail = animalToyTail;
}
@Override
public String toString()
{
return "AnimalToy [animalToyName=" + animalToyName + ", animalToyHead=" + animalToyHead
+ ", animalToyBody=" + animalToyBody + ", animalToyArms=" + animalToyArms
+ ", animalToyLegs=" + animalToyLegs + ", animalToyTail=" + animalToyTail + "]\n";
}
}
AnimalToyBuilder.java
public abstract class AnimalToyBuilder
{
private AnimalToy animalToy;
public AnimalToy getAnimalToy()
{
return animalToy;
}
public void setAnimalToy( AnimalToy animalToy )
{
this.animalToy = animalToy;
}
public final AnimalToy buildAnimalToy()
{
AnimalToy animalToy = createAnimalToy();
setAnimalToy(animalToy);
buildAnimalHead();
buildAnimalBody();
buildAnimalLegs();
buildAnimalArms();
buildAnimalTail();
setAnimalToyName();
return animalToy;
}
public abstract void buildAnimalHead();
public abstract void buildAnimalBody();
public abstract void buildAnimalLegs();
public abstract void buildAnimalArms();
public abstract void buildAnimalTail();
public abstract void setAnimalToyName();
public abstract AnimalToy createAnimalToy();
}
DogToyBuilder.java
public class DogToyBuilder extends AnimalToyBuilder
{
public AnimalToy createAnimalToy()
{
return new AnimalToy();
}
public void buildAnimalHead()
{
getAnimalToy().setAnimalToyHead("Dog head");
System.out.println("Step 1 : Dog Head has been built");
}
public void buildAnimalBody()
{
getAnimalToy().setAnimalToyBody("Dog Body");
System.out.println("Step 2 : Dog Body has been built");
}
public void buildAnimalLegs()
{
getAnimalToy().setAnimalToyLegs("Dog 4 legs");
System.out.println("Step 3 : Dog Legs has been built");
}
public void buildAnimalArms()
{
// No implementation because dog doesn't have Arms
getAnimalToy().setAnimalToyLegs("No arms");
System.out.println("Step 4 : is skiped because dog doesn't have Arms");
}
public void setAnimalToyName()
{
getAnimalToy().setAnimalToyName("Dog");
}
public void buildAnimalTail()
{
getAnimalToy().setAnimalToyTail("Dog Tail");
System.out.println("Step 5 : Dog Tail has been built");
}
}
LionToyBuilder.java
public class LionToyBuilder extends AnimalToyBuilder
{
public AnimalToy createAnimalToy()
{
return new AnimalToy();
}
public void buildAnimalHead()
{
getAnimalToy().setAnimalToyHead("Lion head");
System.out.println("Step 1 : Lion Head has been built");
}
public void buildAnimalBody()
{
getAnimalToy().setAnimalToyBody("Lion Body");
System.out.println("Step 2 : Lion Body has been built");
}
public void buildAnimalLegs()
{
getAnimalToy().setAnimalToyLegs("Lion 4 legs");
System.out.println("Step 3 : Lion Legs has been built");
}
public void buildAnimalArms()
{
// No implementation because Lion doesn't have Arms
getAnimalToy().setAnimalToyLegs("No arms");
System.out.println("Step 4 : is skiped because Lion doesn't have Arms");
}
public void setAnimalToyName()
{
getAnimalToy().setAnimalToyName("Lion");
}
public void buildAnimalTail()
{
getAnimalToy().setAnimalToyTail("Lion Tail");
System.out.println("Step 5 : Lion Tail has been built");
}
}
MonkeyToyBuilder.java
public class MonkeyToyBuilder extends AnimalToyBuilder
{
public AnimalToy createAnimalToy()
{
return new AnimalToy();
}
public void buildAnimalHead()
{
getAnimalToy().setAnimalToyHead("Monkey head");
System.out.println("Step 1 : Monkey Head has been built");
}
public void buildAnimalBody()
{
getAnimalToy().setAnimalToyBody("Monkey Body");
System.out.println("Step 2 : Monkey Body has been built");
}
public void buildAnimalLegs()
{
getAnimalToy().setAnimalToyLegs("Monkey 2 legs");
System.out.println("Step 3 : Monkey Legs has been built");
}
public void buildAnimalArms()
{
getAnimalToy().setAnimalToyArms("Monkey 2 Arms");
System.out.println("Step 4 : Monkey Arms has been built");
}
public void setAnimalToyName()
{
getAnimalToy().setAnimalToyName("Monkey");
}
public void buildAnimalTail()
{
getAnimalToy().setAnimalToyTail("Monkey Tail");
System.out.println("Step 5 : Monkey Tail has been built");
}
}
ToyMaker.java
public class ToyMaker
{
public final static String LION_TOY = "Lion";
public final static String DOG_TOY = "Dog";
public final static String MONKEY_TOY = "Monkey";
public static AnimalToy makeToy( String toyType ) throws Exception
{
AnimalToyBuilder animalToyBuilder = null;
if( toyType.equalsIgnoreCase(LION_TOY) )
{
animalToyBuilder = new LionToyBuilder();
}
else if( toyType.equalsIgnoreCase(DOG_TOY) )
{
animalToyBuilder = new DogToyBuilder();
}
else if( toyType.equalsIgnoreCase(MONKEY_TOY) )
{
animalToyBuilder = new MonkeyToyBuilder();
}
else
{
System.out.println("Sorry we cann't make : " + toyType);
throw new Exception("Sorry we cann't make : " + toyType);
}
return animalToyBuilder.buildAnimalToy();
}
}
BuilderClient.java
public class BuilderClient
{
public static void main( String[] args ) throws Exception
{
AnimalToy lionToy = ToyMaker.makeToy(ToyMaker.LION_TOY);
System.out.println(lionToy);
AnimalToy dogToy = ToyMaker.makeToy(ToyMaker.DOG_TOY);
System.out.println(dogToy);
AnimalToy monkeyToy = ToyMaker.makeToy(ToyMaker.MONKEY_TOY);
System.out.println(monkeyToy);
}
}
Output
Step 1 : Lion Head has been built
Step 2 : Lion Body has been built
Step 3 : Lion Legs has been built
Step 4 : is skiped because Lion doesn't have Arms
Step 5 : Lion Tail has been built
AnimalToy [animalToyName=Lion, animalToyHead=Lion head, animalToyBody=Lion Body, animalToyArms=null, animalToyLegs=No arms, animalToyTail=Lion Tail]
Step 1 : Dog Head has been built
Step 2 : Dog Body has been built
Step 3 : Dog Legs has been built
Step 4 : is skiped because dog doesn't have Arms
Step 5 : Dog Tail has been built
AnimalToy [animalToyName=Dog, animalToyHead=Dog head, animalToyBody=Dog Body, animalToyArms=null, animalToyLegs=No arms, animalToyTail=Dog Tail]
Step 1 : Monkey Head has been built
Step 2 : Monkey Body has been built
Step 3 : Monkey Legs has been built
Step 4 : Monkey Arms has been built
Step 5 : Monkey Tail has been built
AnimalToy [animalToyName=Monkey, animalToyHead=Monkey head, animalToyBody=Monkey Body, animalToyArms=Monkey 2 Arms, animalToyLegs=Monkey 2 legs, animalToyTail=Monkey Tail]
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