Java实现构建器模式的最佳方法

Question

public class Person {
    private String firstName;
    // other properties ...

    private Person() {}

    // getters ...

    public static class Builder {
        // person object instead of all the person properties
        private Person person;

        public Builder() {
            person = new Person();
        }

        public Builder setFirstName(String firstName) {
            person.firstName = firstName;

            return this;
        }

        // other setters ...

        public Person build() {
            if (null == person.firstName) {
                throw new IllegalStateException("Invalid data.");
            }

            return person;
        }
    }
}

public class Person {
    private String firstName;
    // other properties ...

    private Person() {}

    // getters ...

    public static class Builder {
        // person properties instead of object
        private String firstName;
        // other properties ...

        public Builder() {}

        public Builder setFirstName(String firstName) {
            this.firstName = firstName;

            return this;
        }

        // other setters ...

        public Person build() {
            if (null == this.firstName) {
                throw new IllegalStateException("Invalid data.");
            }

            Person person = new Person();
            person.firstName = firstName;

            return person;
        }
    }
}

我更喜欢第一种方式，因为我认为在构建器中重复它们是多余的。第一种方法是否存在一些缺点？

提前谢谢，抱歉我的英语不好。

Answer 1

小提示：是的，这些属性可能是重复的，但它们有优点

下面的细节：如果你看这里的细节。

Pizza pizza = new Pizza(12);
pizza.setCheese(true);
pizza.setPepperoni(true);
pizza.setBacon(true);

这里的问题是，因为对象是通过几次调用创建的，所以它在构造过程中可能处于不一致的状态。这也需要很多额外的努力来确保线程安全。

 public static class Builder {

    public Pizza build() {    // Notice this method
      return new Pizza(this);
    }
  }

  private Pizza(Builder builder) {  // Notice this Constructor
    size = builder.size;
    cheese = builder.cheese;
    pepperoni = builder.pepperoni;
    bacon = builder.bacon;
  }