• Source: cipher
  • ciphermagic.cn/java8-builder.html

Programmers often encounter soul-searching questions: Do you have a partner?

No, but I can get a new one!

public class GirlFriend { private String name; private int age; // Omit getter & setter... public static void main(String[] args) { GirlFriend myGirlFriend = new GirlFriend(); MyGirlFriend. Elegantly-named setName (" small beautiful "); myGirlFriend.setAge(18); }}

No problem, brother! But what if the object has too many attributes?

public class GirlFriend { private String name; private int age; private int bust; private int waist; private int hips; private List<String> hobby; private String birthday; private String address; private String mobile; private String email; private String hairColor; private Map<String, String> gift; // Wait... // Omit getter & setter... public static void main(String[] args) { GirlFriend myGirlFriend = new GirlFriend(); MyGirlFriend. Elegantly-named setName (" small beautiful "); myGirlFriend.setAge(18); myGirlFriend.setBust(33); myGirlFriend.setWaist(23); myGirlFriend.setHips(33); myGirlFriend.setBirthday("2001-10-26"); MyGirlfriend.setAddress (" Shanghai Pudong "); myGirlFriend.setMobile("18688888888"); myGirlFriend.setEmail("[email protected]"); MyGirlFriend. SetHairColor (" light ribbon point micro volume "); List<String> hobby = new ArrayList<>(); Hobby. Add (" shopping "); Hobby. Add (" shopping "); Hobby. add(" buy something "); myGirlFriend.setHobby(hobby); Map<String, String> gift = new HashMap<>(); Put (" Valentine's Day ", "LBR 1912 Queen's Age "); Put (" birthday gift ", "Dior flame blue gold "); Put (" Memorial Day Gift ", "Armani Red Tube Lip Glaze "); myGirlFriend.setGift(gift); // Wait... }}

—

Girlfriend {name=' 2001-10-26', age=18, bust=33, waist=23, hips=33, hobby=[shopping, shopping, shopping], birthday='2001-10-26', Address =' Shanghai Pudong ', Mobile ='18688888888', Email ='[email protected]', hairColor=' light brown with little curls', Gift ={Valentine's Day Gift =LBR 1912 Queen's Age, Birthday gift = Dior flame blue gold, anniversary gift = Armani red tube lip glaze}}

Girlfriend is beautiful, but it’s hard to write.

Disadvantages: Separating instantiation from setting properties is hard to maintain; The variable name is written repeatedly.

Don’t panic, see the magic weapon ~

Here will not introduce other Builder implementation, directly dedicated to the most practical general Builder:

Applies to all classes, no modification of the original class is required, and Lombok plug-in support is not required.

First look at the posture:

Public Class Girlfriend {// Girlfriend is the best friend. // Omit getter & setter... // For demonstration purposes, Public void addHobby(String Hobby) {this.Hobby = optional.ofNullable (this.Hobby).oRelse (new ArrayList<>()); this.hobby.add(hobby); } public void addGift(String day, String gift) { this.gift = Optional.ofNullable(this.gift).orElse(new HashMap<>()); this.gift.put(day, gift); } public void setVitalStatistics(int bust, int waist, int hips) { this.bust = bust; this.waist = waist; this.hips = hips; } public static void main(String[] args) { GirlFriend myGirlFriend = Builder.of(GirlFriend::new) With (GirlFriend: : elegantly-named setName, "small beautiful"), with (GirlFriend: : setAge, 18) with (GirlFriend: : setVitalStatistics, 33, 23, With (Girlfriend ::setBirthday, "2001-10-26"). With (Girlfriend ::setAddress, "Shanghai ::setAddress "). "18688888888") .with(GirlFriend::setEmail, "[email protected]") .with(GirlFriend::setHairColor, "Light brown with slight curls "). With (Girlfriend :: AddHobby," Shopping "). With (Girlfriend :: AddHobby, "Shopping "). "Shopping "). With (GirlFriend::addGift, "LBR 1912 queen "). With (GirlFriend::addGift," birthday present ", "Dior Flame Blue and Gold ").with(Girlfriend ::addGift," anniversary gift ", "Armani Red tube lip glaze ") // blah blah blah... .build(); }}

See! Instantiation and property set in the same statement, chain operation, all the way dot dot, cool!

Talk is cheap, show me the code

/** * Generic Builder pattern Builder ** @Author: CipherCui * @since 2019/8/29 */ public class Builder<T> { private final Supplier<T> instantiator; private List<Consumer<T>> modifiers = new ArrayList<>(); public Builder(Supplier<T> instantiator) { this.instantiator = instantiator; } public static <T> Builder<T> of(Supplier<T> instantiator) { return new Builder<>(instantiator); } public <P1> Builder<T> with(Consumer1<T, P1> consumer, P1 p1) { Consumer<T> c = instance -> consumer.accept(instance, p1); modifiers.add(c); return this; } public <P1, P2> Builder<T> with(Consumer2<T, P1, P2> consumer, P1 p1, P2 p2) { Consumer<T> c = instance -> consumer.accept(instance, p1, p2); modifiers.add(c); return this; } public <P1, P2, P3> Builder<T> with(Consumer3<T, P1, P2, P3> consumer, P1 p1, P2 p2, P3 p3) { Consumer<T> c = instance -> consumer.accept(instance, p1, p2, p3); modifiers.add(c); return this; } public T build() { T value = instantiator.get(); modifiers.forEach(modifier -> modifier.accept(value)); modifiers.clear(); return value; } /** * 1 Consumer */ @FunctionalInterface public interface Consumer1<T, P1> {void accept(T T, P1 P1); } / Consumer * / * * * 2 parameter @ FunctionalInterface public interface Consumer2 < T, P1, P2 > {void the accept (T, T, P1 P1, P2 P2); } / Consumer * / * * * 3 parameter @ FunctionalInterface public interface Consumer3 < T, P1, P2, P3 > {void the accept (T, T, P1 P1, P2 p2, P3 p3); }}

This example supports a set property method with up to three parameters, which is quite sufficient. If you want to extend it, it’s easy to follow suit and add a Consumer with multiple parameters.

Use your Builder to create an object

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