程式員經常會遇到靈魂拷問：你有對象嗎？
沒有，但我可以 new 一個！
publicclass GirlFriend {
private String name;
privateint age;
// 省略 getter & setter ...
public static void main(String[] args) {
GirlFriend myGirlFriend = new GirlFriend();
myGirlFriend.setName("小美");
myGirlFriend.setAge(18);
}
}
沒問題，老鐵！但如果對象的屬性太多，咋辦？
publicclass GirlFriend {
private String name;
privateint age;
privateint bust;
privateint waist;
privateint hips;
private List hobby;
private String birthday;
private String address;
private String mobile;
private String email;
private String hairColor;
private Map gift;
// 等等等等 ...
// 省略 getter & setter ...
public static void main(String[] args) {
GirlFriend myGirlFriend = new GirlFriend();
myGirlFriend.setName("小美");
myGirlFriend.setAge(18);
myGirlFriend.setBust(33);
myGirlFriend.setWaist(23);
myGirlFriend.setHips(33);
myGirlFriend.setBirthday("2001-10-26");
myGirlFriend.setAddress("上海浦東");
myGirlFriend.setMobile("18688888888");
myGirlFriend.setEmail("[email protected]");
myGirlFriend.setHairColor("淺棕色帶點微卷");
List hobby = new ArrayList<>();
hobby.add("逛街");
hobby.add("購物");
hobby.add("買東西");
myGirlFriend.setHobby(hobby);
Map gift = new HashMap<>();
gift.put("情人節禮物", "LBR 1912女王時代");
gift.put("生日禮物", "迪奧烈焰藍金");
gift.put("紀念日禮物", "阿瑪尼紅管唇釉");
myGirlFriend.setGift(gift);
// 等等等等 ...
}
}
GirlFriend{name='小美'
, age=18
, bust=33
, waist=23
, hips=33
, hobby=[逛街, 購物, 買東西]
, birthday='2001-10-26'
, address='上海浦東'
, mobile='18688888888'
, email='[email protected]'
, hairColor='淺棕色帶點微卷'
, gift={情人節禮物=LBR 1912女王時代, 生日禮物=迪奧烈焰藍金, 紀念日禮物=阿瑪尼紅管唇釉}
}
GirlFriend 是很美，但寫起來也太麻煩了吧。
說說缺點：執行個體化和設定屬性分開，不好維護；變量名重複寫。
莫慌，看法寶~
這裡不再介紹其他 Builder 實作方式，直接祭出最實用的通用Builder：
适用于所有類，不需要改造原來類，不需要 lombok 插件支援。
先看看使用姿勢：
publicclass GirlFriend {
// 省略屬性 ...
// 省略 getter & setter ...
// 為了示範友善，加幾個聚合方法
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::setName, "小美")
.with(GirlFriend::setAge, 18)
.with(GirlFriend::setVitalStatistics, 33, 23, 33)
.with(GirlFriend::setBirthday, "2001-10-26")
.with(GirlFriend::setAddress, "上海浦東")
.with(GirlFriend::setMobile, "18688888888")
.with(GirlFriend::setEmail, "[email protected]")
.with(GirlFriend::setHairColor, "淺棕色帶點微卷")
.with(GirlFriend::addHobby, "逛街")
.with(GirlFriend::addHobby, "購物")
.with(GirlFriend::addHobby, "買東西")
.with(GirlFriend::addGift, "情人節禮物", "LBR 1912女王時代")
.with(GirlFriend::addGift, "生日禮物", "迪奧烈焰藍金")
.with(GirlFriend::addGift, "紀念日禮物", "阿瑪尼紅管唇釉")
// 等等等等 ...
.build();
}
}
看到了嗎！執行個體化和屬性設定在同一條語句執行，鍊式操作，一路點點點，清爽！
Talk is cheap, show me the code：
publicclass Builder {
privatefinal Supplier instantiator;
private List> modifiers = new ArrayList<>();
public Builder(Supplier instantiator) {
this.instantiator = instantiator;
}
publicstatic Builder of(Supplier instantiator) {
returnnew Builder<>(instantiator);
}
public Builder with(Consumer1 consumer, P1 p1) {
Consumer c = instance -> consumer.accept(instance, p1);
modifiers.add(c);
returnthis;
}
public Builder with(Consumer2 consumer, P1 p1, P2 p2) {
Consumer c = instance -> consumer.accept(instance, p1, p2);
modifiers.add(c);
returnthis;
}
public Builder with(Consumer3 consumer, P1 p1, P2 p2, P3 p3) {
Consumer c = instance -> consumer.accept(instance, p1, p2, p3);
modifiers.add(c);
returnthis;
}
public T build() {
T value = instantiator.get();
modifiers.forEach(modifier -> modifier.accept(value));
modifiers.clear();
return value;
}
@FunctionalInterface
publicinterface Consumer1 {
void accept(T t, P1 p1);
}
@FunctionalInterface
publicinterface Consumer2 {
void accept(T t, P1 p1, P2 p2);
}
@FunctionalInterface
publicinterface Consumer3 {
void accept(T t, P1 p1, P2 p2, P3 p3);
}
}
這個示例最多支援三個參數的設定屬性方法，也完全夠用了。如果要擴充也很容易，依葫蘆畫瓢，添加多個參數的Consumer。
快用你的 Builder 建個對象吧~
來源：cipher