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Nicolai Parlog
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[02] Demonstrate builders and show alternatives
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‎README.md‎

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* Item 1: [Consider static factory methods instead of constructors](https://www.youtube.com/watch?v=WUROOKn2OTk) -
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[examples](src/main/java/org/codefx/demo/effective_java/_01_static_factory_methods/Main.java)
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* Item 2: [Consider a builder when faced with many constructor parameters](https://www.youtube.com/watch?v=2GMp8VuxZnw)

‎src/main/java/org/codefx/demo/effective_java/_02_builder_pattern/Main.java‎

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package org.codefx.demo.effective_java._02_builder_pattern;
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import org.codefx.demo.effective_java._02_builder_pattern.SelfTypes.Employee;
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import org.codefx.demo.effective_java._02_builder_pattern.SelfTypes.EmployeeBuilder;
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import org.codefx.demo.effective_java._02_builder_pattern.SelfTypes.Freelancer;
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import org.codefx.demo.effective_java._02_builder_pattern.SelfTypes.FreelancerBuilder;
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import org.codefx.demo.effective_java._02_builder_pattern.TowardsDsl.Body;
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import org.codefx.demo.effective_java._02_builder_pattern.TowardsDsl.Car;
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import org.codefx.demo.effective_java._02_builder_pattern.TowardsDsl.CarFactory;
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import org.codefx.demo.effective_java._02_builder_pattern.TowardsDsl.ConvertibleBody;
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import org.codefx.demo.effective_java._02_builder_pattern.TowardsDsl.Decal;
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import org.codefx.demo.effective_java._02_builder_pattern.TowardsDsl.Paint;
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import org.codefx.demo.effective_java._02_builder_pattern.TowardsDsl.RearSpoiler;
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import org.codefx.demo.effective_java._02_builder_pattern.TowardsDsl.RoofSpoiler;
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import org.codefx.demo.effective_java._02_builder_pattern.TowardsDsl.Tires;
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/*
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* You will find NOTEs on the following topics:
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* - alternatives
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* - DSL
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* - self type
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* - refactoring
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*/
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public class Main {
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public static void main(String[] args) {
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towardsDsl();
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selfType();
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}
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private static void towardsDsl() {
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Car car = new CarFactory()
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.body(new Body())
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.spoiler(new RoofSpoiler())
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.paint(new Paint())
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.decal(new Decal())
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.tires(new Tires())
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.build();
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Car convertible = new CarFactory()
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.body(new ConvertibleBody())
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// can't add a roof spoiler!
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.spoiler(new RearSpoiler())
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.paint(new Paint())
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.decal(new Decal())
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.tires(new Tires())
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.build();
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}
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private static void selfType() {
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Employee john = new EmployeeBuilder()
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.name("John Doe")
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.address("Paris")
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.build();
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Freelancer jane = new FreelancerBuilder()
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.name("Jane Doe")
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.address("Paris")
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.build();
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}
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}

‎src/main/java/org/codefx/demo/effective_java/_02_builder_pattern/NutritionFacts.kt‎

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/*
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package org.codefx.demo.effective_java._02_builder_pattern
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class NutritionFacts(
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val servingSize: Int,
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val servings: Int,
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val fat: Int = 0,
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val sodium: Int = 0,
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val carbohydrates: Int = 0) { }
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fun main(args: Array<String>) {
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val facts = NutritionFacts(
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servingSize = 150, servings = 4,
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fat = 20, carbohydrates = 25);
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}
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*/

‎src/main/java/org/codefx/demo/effective_java/_02_builder_pattern/RefactorToBuilder.java‎

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package org.codefx.demo.effective_java._02_builder_pattern;
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// NOTE refactoring: Your IDE should help you refactor from constructor to builder.
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public class RefactorToBuilder {
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public static void main(String[] args) {
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Person p = new Person("Jane Doe");
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System.out.println(p);
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}
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public static class Person {
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private final String name;
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public Person(String name) {
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this.name = name;
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}
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}
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}

‎src/main/java/org/codefx/demo/effective_java/_02_builder_pattern/SelfTypes.java‎

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package org.codefx.demo.effective_java._02_builder_pattern;
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public class SelfTypes {
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public abstract static class Person {
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private final String name;
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private final String address;
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protected Person(PersonBuilder<?, ?> builder) {
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this.name = builder.name;
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this.address = builder.address;
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}
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public String name() {
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return name;
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}
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public String address() {
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return address;
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}
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}
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public static class Employee extends Person {
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private Employee(EmployeeBuilder builder) {
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super(builder);
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}
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}
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public static class Freelancer extends Person {
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private Freelancer(FreelancerBuilder builder) {
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super(builder);
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}
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}
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// NOTE self type:
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// With a recursive generic type `SELF extends PersonBuilder<SELF>` (ignoring `P` for a moment,
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// which does not pertain to this), it is possible to capture "type of this instance".
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public static abstract class PersonBuilder<P extends Person, SELF extends PersonBuilder<P, SELF>> {
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protected String name;
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protected String address;
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// NOTE self type:
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// Thanks to `SELF`, `name(String)` can express that it returns not just a `PersonBuilder`,
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// but an instance of the concrete builder it was called on.
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public SELF name(String name) {
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this.name = name;
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// NOTE self type:
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// This cast is safe, so I find it tolerable. See below for an alternative.
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return (SELF) this;
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}
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// NOTE self type:
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// To avoid the casts `(SELF) this`, call this method instead.
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// protected abstract SELF self();
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public SELF address(String address) {
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this.address = address;
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return (SELF) this;
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}
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public abstract P build();
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}
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public static class EmployeeBuilder extends PersonBuilder<Employee, EmployeeBuilder> {
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@Override
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public Employee build() {
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return new Employee(this);
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}
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// NOTE self type:
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// Here's how to implement `self()` in a concrete builder.
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// @Override
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// protected EmployeeBuilder self() {
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// return this;
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// }
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}
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public static class FreelancerBuilder extends PersonBuilder<Freelancer, FreelancerBuilder> {
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@Override
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public Freelancer build() {
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return new Freelancer(this);
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}
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}
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}

‎src/main/java/org/codefx/demo/effective_java/_02_builder_pattern/TowardsDsl.java‎

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package org.codefx.demo.effective_java._02_builder_pattern;
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// NOTE DSL:
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// The common approach to a builder is to have a single class, on which `build()` can be called
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// at any time. If the provided information was incomplete, a `RuntimeException` is the result.
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//
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// The `CarFactory` in this class follows a more powerful/complex approach where each required
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// "setter" transitions to a new type of builder and only the last one has a `build()` method.
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// This way, other constructors/methods can use types for their parameters that represent a
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// specific "phase" of the build process. The progression from empty to complete builder is thus
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// encoded in the type system, which means the compiler can check errors that would otherwise
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// only be discovered at run time.
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public class TowardsDsl {
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public static class Car {
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private final Body body;
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private final Spoiler spoiler;
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private final Paint paint;
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private final Decal decal;
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private final Tires tires;
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private Car(WithPaintedBodyAndTires builder) {
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this.body = builder.body;
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this.spoiler = builder.spoiler;
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this.paint = builder.paint;
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this.decal = builder.decal;
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this.tires = builder.tires;
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}
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}
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public static class Body { }
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public static class ConvertibleBody extends Body { }
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public static class Spoiler { }
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public static class RoofSpoiler extends Spoiler { }
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public static class RearSpoiler extends Spoiler { }
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public static class Paint { }
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public static class Decal { }
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public static class Tires { }
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public static class CarFactory {
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// NOTE DSL: This method returns `WithBody` instead of a `CarFactory`.
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public WithBody body(Body body) {
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return new WithBody(body);
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}
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public WithConvertibleBody body(ConvertibleBody body) {
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return new WithConvertibleBody(body);
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}
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// NOTE self type:
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// There is no `build()` method here, because without body, the car is incomplete.
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}
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public static class WithBody {
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private final Body body;
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private Spoiler spoiler;
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public WithBody(Body body) {
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this.body = body;
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}
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public WithBody spoiler(Spoiler spoiler) {
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this.spoiler = spoiler;
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return this;
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}
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public WithPaintedBody paint(Paint paint) {
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return new WithPaintedBody(body, spoiler, paint);
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}
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}
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public static class WithConvertibleBody {
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private final ConvertibleBody body;
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private RearSpoiler spoiler;
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public WithConvertibleBody(ConvertibleBody body) {
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this.body = body;
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}
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public WithConvertibleBody spoiler(RearSpoiler spoiler) {
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this.spoiler = spoiler;
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return this;
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}
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public WithPaintedBody paint(Paint paint) {
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return new WithPaintedBody(body, spoiler, paint);
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}
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}
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public static class WithPaintedBody {
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private final Body body;
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private final Spoiler spoiler;
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private final Paint paint;
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private Decal decal;
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public WithPaintedBody(Body body, Spoiler spoiler, Paint paint) {
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this.body = body;
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this.spoiler = spoiler;
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this.paint = paint;
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}
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public WithPaintedBody decal(Decal decal) {
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this.decal = decal;
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return this;
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}
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public WithPaintedBodyAndTires tires(Tires tires) {
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return new WithPaintedBodyAndTires(body, spoiler, paint, decal, tires);
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}
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}
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public static class WithPaintedBodyAndTires {
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private final Body body;
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private final Spoiler spoiler;
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private final Paint paint;
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private final Decal decal;
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private final Tires tires;
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public WithPaintedBodyAndTires(Body body, Spoiler spoiler, Paint paint, Decal decal, Tires tires) {
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this.body = body;
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this.spoiler = spoiler;
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this.paint = paint;
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this.tires = tires;
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this.decal = decal;
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}
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public Car build() {
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return new Car(this);
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}
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}
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}

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