参考：http://www.importnew.com/6605.html

  • Builder会增加个类代码，这也意味着开发者在给类增加属性时有时会忘记给该属性添加支持的builder。为了克服这个问题，通常我会将builder嵌套到类中，这样可以很容易地发现哪个相关的builder需要更新

  • 构建对象时，如果碰到类有很多参数——其中很多参数类型相同而且很多参数可以为空时，我更喜欢Builder模式来完成。当参数数量不多、类型不同而且都是必须出现时，通过增加代码实现Builder往往无法体现它的优势。在这种情况下，理想的方法是调用传统的构造函数。再者，如果不需要保持不变，那么就使用无参构造函数调用相应的set方法吧。

  • 必要参数写到构造器里

  • 如果要实现builder的重用性，可以讲初始化工作放到目标类中。不需要重用的话，可以讲初始化工作在builde创建出来的时候，就将实例创建出来。

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package dustin.examples;
 
/**
 * Person class used as part of too many parameters demonstration.
 * 
 * @author Dustin
 */
public class Person
{
   private final String lastName;
   private final String firstName;
   private final String middleName;
   private final String salutation;
   private final String suffix;
   private final String streetAddress;
   private final String city;
   private final String state;
   private final boolean isFemale;
   private final boolean isEmployed;
   private final boolean isHomewOwner;
 
   public Person(
      final String newLastName,
      final String newFirstName,
      final String newMiddleName,
      final String newSalutation,
      final String newSuffix,
      final String newStreetAddress,
      final String newCity,
      final String newState,
      final boolean newIsFemale,
      final boolean newIsEmployed,
      final boolean newIsHomeOwner)
   {
      this.lastName = newLastName;
      this.firstName = newFirstName;
      this.middleName = newMiddleName;
      this.salutation = newSalutation;
      this.suffix = newSuffix;
      this.streetAddress = newStreetAddress;
      this.city = newCity;
      this.state = newState;
      this.isFemale = newIsFemale;
      this.isEmployed = newIsEmployed;
      this.isHomewOwner = newIsHomeOwner;
   }
 
   public static class PersonBuilder
   {
      private String nestedLastName;
      private String nestedFirstName;
      private String nestedMiddleName;
      private String nestedSalutation;
      private String nestedSuffix;
      private String nestedStreetAddress;
      private String nestedCity;
      private String nestedState;
      private boolean nestedIsFemale;
      private boolean nestedIsEmployed;
      private boolean nestedIsHomeOwner;
 
      public PersonBuilder(
         final String newFirstName,
         final String newCity,
         final String newState) 
      {
         this.nestedFirstName = newFirstName;
         this.nestedCity = newCity;
         this.nestedState = newState;
      }
 
      public PersonBuilder lastName(String newLastName)
      {
         this.nestedLastName = newLastName;
         return this;
      }
 
      public PersonBuilder firstName(String newFirstName)
      {
         this.nestedFirstName = newFirstName;
         return this;
      }
 
      public PersonBuilder middleName(String newMiddleName)
      {
         this.nestedMiddleName = newMiddleName;
         return this;
      }
 
      public PersonBuilder salutation(String newSalutation)
      {
         this.nestedSalutation = newSalutation;
         return this;
      }
 
      public PersonBuilder suffix(String newSuffix)
      {
         this.nestedSuffix = newSuffix;
         return this;
      }
 
      public PersonBuilder streetAddress(String newStreetAddress)
      {
         this.nestedStreetAddress = newStreetAddress;
         return this;
      }
 
      public PersonBuilder city(String newCity)
      {
         this.nestedCity = newCity;
         return this;
      }
 
      public PersonBuilder state(String newState)
      {
         this.nestedState = newState;
         return this;
      }
 
      public PersonBuilder isFemale(boolean newIsFemale)
      {
         this.nestedIsFemale = newIsFemale;
         return this;
      }
 
      public PersonBuilder isEmployed(boolean newIsEmployed)
      {
         this.nestedIsEmployed = newIsEmployed;
         return this;
      }
 
      public PersonBuilder isHomeOwner(boolean newIsHomeOwner)
      {
         this.nestedIsHomeOwner = newIsHomeOwner;
         return this;
      }
 
      public Person createPerson()
      {
         return new Person(
            nestedLastName, nestedFirstName, nestedMiddleName,
            nestedSalutation, nestedSuffix,
            nestedStreetAddress, nestedCity, nestedState,
            nestedIsFemale, nestedIsEmployed, nestedIsHomeOwner);
      }
   }
}