設計模式 -- 建造者模式

一步一步流式地構建複雜對象.

建造者模式（Builder Pattern）使用多個簡單的對象一步一步構建成一個複雜的對象。這種類型的設計模式屬於建立型模式，它提供了一種建立對象的最佳方式。

一個 Builder 類會一步一步構造最終的對象。該 Builder 類是獨立於其餘對象的。

寫法

不使用建造者模式

class Hero{
  // 複雜的構造方法
  public Hero(Profession profession, String name, HairType hairType, HairColor hairColor, Armor armor, Weapon weapon) {
  }
  
}  
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使用Builder模式

最終被構建的類.使用Builder做爲構造方法參數

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;
  }
}
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Builder類

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);
    }
  }
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使用

Hero mage = new Hero.Builder(Profession.MAGE,"Riobard")
  .withHairColor(HairColor.BLACK)
  .withWeapon(Weapon.DAGGER)
  .build();
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