建造者模式

建造者模式UML类图

建造者模式java实现

/**
 * Armor enumeration.
 */
public enum Armor {

  CLOTHES("clothes"), LEATHER("leather"), CHAIN_MAIL("chain mail"), PLATE_MAIL("plate mail");

  private final String title;

  Armor(String title) {
    this.title = title;
  }

  @Override
  public String toString() {
    return title;
  }
}

/**
 * HairColor enumeration.
 */
public enum HairColor {

  WHITE, BLOND, RED, BROWN, BLACK;

  @Override
  public String toString() {
    return name().toLowerCase();
  }

}

/**
 * HairType enumeration.
 */
public enum HairType {

  BALD("bald"), SHORT("short"), CURLY("curly"), LONG_STRAIGHT("long straight"), LONG_CURLY(
      "long curly");

  private final String title;

  HairType(String title) {
    this.title = title;
  }

  @Override
  public String toString() {
    return title;
  }
}

/**
 * Profession enumeration.
 */
public enum Profession {

  WARRIOR, THIEF, MAGE, PRIEST;

  @Override
  public String toString() {
    return name().toLowerCase();
  }
}

/**
 * Weapon enumeration.
 */
public enum Weapon {

  DAGGER, SWORD, AXE, WARHAMMER, BOW;

  @Override
  public String toString() {
    return name().toLowerCase();
  }
}

/**
 * Hero, the class with many parameters.
 */
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;
  }

  public Profession getProfession() {
    return profession;
  }

  public String getName() {
    return name;
  }

  public HairType getHairType() {
    return hairType;
  }

  public HairColor getHairColor() {
    return hairColor;
  }

  public Armor getArmor() {
    return armor;
  }

  public Weapon getWeapon() {
    return weapon;
  }

  @Override
  public String toString() {

    var sb = new StringBuilder();
    sb.append("This is a ")
        .append(profession)
        .append(" named ")
        .append(name);
    if (hairColor != null || hairType != null) {
      sb.append(" with ");
      if (hairColor != null) {
        sb.append(hairColor).append(' ');
      }
      if (hairType != null) {
        sb.append(hairType).append(' ');
      }
      sb.append(hairType != HairType.BALD ? "hair" : "head");
    }
    if (armor != null) {
      sb.append(" wearing ").append(armor);
    }
    if (weapon != null) {
      sb.append(" and wielding a ").append(weapon);
    }
    sb.append('.');
    return sb.toString();
  }

  /**
   * The builder class.
   */
  public static class Builder {

    private final Profession profession;
    private final String name;
    private HairType hairType;
    private HairColor hairColor;
    private Armor armor;
    private Weapon weapon;

    /**
     * Constructor.
     */
    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);
    }
  }
}

/**
 * The intention of the Builder pattern is to find a solution to the telescoping constructor
 * anti-pattern. The telescoping constructor anti-pattern occurs when the increase of object
 * constructor parameter combination leads to an exponential list of constructors. Instead of using
 * numerous constructors, the builder pattern uses another object, a builder, that receives each
 * initialization parameter step by step and then returns the resulting constructed object at once.
 *
 * <p>The Builder pattern has another benefit. It can be used for objects that contain flat data
 * (html code, SQL query, X.509 certificate...), that is to say, data that can't be easily edited.
 * This type of data cannot be edited step by step and must be edited at once. The best way to
 * construct such an object is to use a builder class.
 *
 * <p>In this example we have the Builder pattern variation as described by Joshua Bloch in
 * Effective Java 2nd Edition.
 *
 * <p>We want to build {@link Hero} objects, but its construction is complex because of the many
 * parameters needed. To aid the user we introduce {@link Builder} class. {@link Hero.Builder} takes
 * the minimum parameters to build {@link Hero} object in its constructor. After that additional
 * configuration for the {@link Hero} object can be done using the fluent {@link Builder} interface.
 * When configuration is ready the build method is called to receive the final {@link Hero} object.
 */
public class App {

  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);

  /**
   * Program entry point.
   *
   * @param args command line args
   */
  public static void main(String[] args) {

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

    var warrior = new Hero.Builder(Profession.WARRIOR, "Amberjill")
        .withHairColor(HairColor.BLOND)
        .withHairType(HairType.LONG_CURLY).withArmor(Armor.CHAIN_MAIL).withWeapon(Weapon.SWORD)
        .build();
    LOGGER.info(warrior.toString());

    var thief = new Hero.Builder(Profession.THIEF, "Desmond")
        .withHairType(HairType.BALD)
        .withWeapon(Weapon.BOW)
        .build();
    LOGGER.info(thief.toString());

  }
}