158 lines
5.7 KiB
Markdown
158 lines
5.7 KiB
Markdown
---
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layout: pattern
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title: Builder
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folder: builder
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permalink: /patterns/builder/
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categories: Creational
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language: en
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tags:
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- Gang of Four
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---
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## Intent
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Separate the construction of a complex object from its representation so that the same construction
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process can create different representations.
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## Explanation
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Real-world example
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> Imagine a character generator for a role-playing game. The easiest option is to let the computer
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> create the character for you. If you want to manually select the character details like
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> profession, gender, hair color, etc. the character generation becomes a step-by-step process that
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> completes when all the selections are ready.
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In plain words
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> Allows you to create different flavors of an object while avoiding constructor pollution. Useful
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> when there could be several flavors of an object. Or when there are a lot of steps involved in
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> creation of an object.
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Wikipedia says
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> The builder pattern is an object creation software design pattern with the intentions of finding
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> a solution to the telescoping constructor anti-pattern.
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Having said that let me add a bit about what telescoping constructor anti-pattern is. At one point
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or the other, we have all seen a constructor like below:
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```java
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public Hero(Profession profession, String name, HairType hairType, HairColor hairColor, Armor armor, Weapon weapon) {
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}
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```
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As you can see the number of constructor parameters can quickly get out of hand, and it may become
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difficult to understand the arrangement of parameters. Plus this parameter list could keep on
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growing if you would want to add more options in the future. This is called telescoping constructor
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anti-pattern.
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**Programmatic Example**
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The sane alternative is to use the Builder pattern. First of all, we have our hero that we want to
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create:
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```java
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public final class Hero {
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private final Profession profession;
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private final String name;
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private final HairType hairType;
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private final HairColor hairColor;
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private final Armor armor;
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private final Weapon weapon;
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private Hero(Builder builder) {
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this.profession = builder.profession;
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this.name = builder.name;
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this.hairColor = builder.hairColor;
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this.hairType = builder.hairType;
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this.weapon = builder.weapon;
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this.armor = builder.armor;
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}
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}
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```
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Then we have the builder:
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```java
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public static class Builder {
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private final Profession profession;
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private final String name;
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private HairType hairType;
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private HairColor hairColor;
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private Armor armor;
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private Weapon weapon;
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public Builder(Profession profession, String name) {
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if (profession == null || name == null) {
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throw new IllegalArgumentException("profession and name can not be null");
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}
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this.profession = profession;
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this.name = name;
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}
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public Builder withHairType(HairType hairType) {
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this.hairType = hairType;
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return this;
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}
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public Builder withHairColor(HairColor hairColor) {
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this.hairColor = hairColor;
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return this;
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}
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public Builder withArmor(Armor armor) {
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this.armor = armor;
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return this;
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}
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public Builder withWeapon(Weapon weapon) {
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this.weapon = weapon;
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return this;
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}
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public Hero build() {
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return new Hero(this);
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}
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}
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```
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Then it can be used as:
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```java
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var mage = new Hero.Builder(Profession.MAGE, "Riobard").withHairColor(HairColor.BLACK).withWeapon(Weapon.DAGGER).build();
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```
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## Class diagram
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## Applicability
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Use the Builder pattern when
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* The algorithm for creating a complex object should be independent of the parts that make up the object and how they're assembled
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* The construction process must allow different representations for the object that's constructed
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## Tutorials
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* [Refactoring Guru](https://refactoring.guru/design-patterns/builder)
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* [Oracle Blog](https://blogs.oracle.com/javamagazine/post/exploring-joshua-blochs-builder-design-pattern-in-java)
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* [Journal Dev](https://www.journaldev.com/1425/builder-design-pattern-in-java)
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## Known uses
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* [java.lang.StringBuilder](http://docs.oracle.com/javase/8/docs/api/java/lang/StringBuilder.html)
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* [java.nio.ByteBuffer](http://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html#put-byte-) as well as similar buffers such as FloatBuffer, IntBuffer and so on.
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* [java.lang.StringBuffer](http://docs.oracle.com/javase/8/docs/api/java/lang/StringBuffer.html#append-boolean-)
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* All implementations of [java.lang.Appendable](http://docs.oracle.com/javase/8/docs/api/java/lang/Appendable.html)
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* [Apache Camel builders](https://github.com/apache/camel/tree/0e195428ee04531be27a0b659005e3aa8d159d23/camel-core/src/main/java/org/apache/camel/builder)
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* [Apache Commons Option.Builder](https://commons.apache.org/proper/commons-cli/apidocs/org/apache/commons/cli/Option.Builder.html)
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## Credits
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* [Design Patterns: Elements of Reusable Object-Oriented Software](https://www.amazon.com/gp/product/0201633612/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0201633612&linkCode=as2&tag=javadesignpat-20&linkId=675d49790ce11db99d90bde47f1aeb59)
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* [Effective Java](https://www.amazon.com/gp/product/0134685997/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0134685997&linkCode=as2&tag=javadesignpat-20&linkId=4e349f4b3ff8c50123f8147c828e53eb)
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* [Head First Design Patterns: A Brain-Friendly Guide](https://www.amazon.com/gp/product/0596007124/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596007124&linkCode=as2&tag=javadesignpat-20&linkId=6b8b6eea86021af6c8e3cd3fc382cb5b)
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* [Refactoring to Patterns](https://www.amazon.com/gp/product/0321213351/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0321213351&linkCode=as2&tag=javadesignpat-20&linkId=2a76fcb387234bc71b1c61150b3cc3a7)
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