builder/README.md
The Builder design pattern in Java, a fundamental creational pattern, allows for the step-by-step construction of complex objects. It separates the construction of a complex object from its representation so that the same construction process can create different representations.
Real-world example
The Java Builder pattern is particularly useful in scenarios where object creation involves numerous parameters.
Imagine you are building a customizable sandwich at a deli. The Builder design pattern in this context would involve a SandwichBuilder that allows you to specify each component of the sandwich, such as the type of bread, meat, cheese, vegetables, and condiments. Instead of having to know how to construct the sandwich from scratch, you use the SandwichBuilder to add each desired component step-by-step, ensuring you get exactly the sandwich you want. This separation of construction from the final product representation ensures that the same construction process can yield different types of sandwiches based on the specified components.
In plain words
Allows you to create different flavors of an object while avoiding constructor pollution. Useful when there could be several flavors of an object. Or when there are a lot of steps involved in creation of an object.
Wikipedia says
The builder pattern is an object creation software design pattern with the intentions of finding a solution to the telescoping constructor antipattern.
With that in mind, let's explain what the telescoping constructor antipattern is. At some point, we have all encountered a constructor like the one below:
public Hero(Profession profession,String name,HairType hairType,HairColor hairColor,Armor armor,Weapon weapon){
// Value assignments
}
As you can see, the number of constructor parameters can quickly become overwhelming, making it difficult to understand their arrangement. Additionally, this list of parameters might continue to grow if you decide to add more options in the future. This is known as the telescoping constructor antipattern.
Sequence diagram
In this Java Builder pattern example, we construct different types of Hero objects with varying attributes.
Imagine a character generator for a role-playing game. The simplest option is to let the computer generate the character for you. However, if you prefer to manually select character details such as profession, gender, hair color, etc., the character creation becomes a step-by-step process that concludes once all selections are made.
A more sensible approach is to use the Builder pattern. First, let's consider the Hero that we want to create:
public final class Hero {
private final Profession profession;
private final String name;
private final HairType hairType;
private final HairColor hairColor;
private final Armor armor;
private final Weapon weapon;
private Hero(Builder builder) {
this.profession = builder.profession;
this.name = builder.name;
this.hairColor = builder.hairColor;
this.hairType = builder.hairType;
this.weapon = builder.weapon;
this.armor = builder.armor;
}
}
Then we have the Builder:
public static class Builder {
private final Profession profession;
private final String name;
private HairType hairType;
private HairColor hairColor;
private Armor armor;
private Weapon weapon;
public Builder(Profession profession, String name) {
if (profession == null || name == null) {
throw new IllegalArgumentException("profession and name can not be null");
}
this.profession = profession;
this.name = name;
}
public Builder withHairType(HairType hairType) {
this.hairType = hairType;
return this;
}
public Builder withHairColor(HairColor hairColor) {
this.hairColor = hairColor;
return this;
}
public Builder withArmor(Armor armor) {
this.armor = armor;
return this;
}
public Builder withWeapon(Weapon weapon) {
this.weapon = weapon;
return this;
}
public Hero build() {
return new Hero(this);
}
}
Then it can be used as:
public static void main(String[] args) {
var mage = new Hero.Builder(Profession.MAGE, "Riobard")
.withHairColor(HairColor.BLACK)
.withWeapon(Weapon.DAGGER)
.build();
LOGGER.info(mage.toString());
var warrior = new Hero.Builder(Profession.WARRIOR, "Amberjill")
.withHairColor(HairColor.BLOND)
.withHairType(HairType.LONG_CURLY).withArmor(Armor.CHAIN_MAIL).withWeapon(Weapon.SWORD)
.build();
LOGGER.info(warrior.toString());
var thief = new Hero.Builder(Profession.THIEF, "Desmond")
.withHairType(HairType.BALD)
.withWeapon(Weapon.BOW)
.build();
LOGGER.info(thief.toString());
}
Program output:
16:28:06.058 [main] INFO com.iluwatar.builder.App -- This is a mage named Riobard with black hair and wielding a dagger.
16:28:06.060 [main] INFO com.iluwatar.builder.App -- This is a warrior named Amberjill with blond long curly hair wearing chain mail and wielding a sword.
16:28:06.060 [main] INFO com.iluwatar.builder.App -- This is a thief named Desmond with bald head and wielding a bow.
Use the Builder pattern when
Benefits:
Trade-offs: