Build模式

public class User {
    private final String name;        //必选,由final修饰，属性不可修改
    private final String cardID;      //必选
    private final int age;            //可选
    private final String address;      //可选
    private final String phone;        //可选

    private User(UserBuilder userBuilder){      ／／user类的构造函数为私有的
        this.name=userBuilder.name;
        this.cardID=userBuilder.cardID;
        this.age=userBuilder.age;
        this.address=userBuilder.address;
        this.phone=userBuilder.phone;
    }

    public String getName() {
        return name;
    }

    public String getCardID() {
        return cardID;
    }

    public int getAge() {
        return age;
    }

    public String getAddress() {
        return address;
    }

    public String getPhone() {
        return phone;
    }

    public static class UserBuilder{
        private final String name;    ／／必选对象用final修饰
        private final String cardID;
        private int age;
        private String address;
        private String phone;

        public UserBuilder(String name,String cardID){ ／／构造方法只接受必传的参数
            this.name=name;
            this.cardID=cardID;
        }

        public UserBuilder age(int age){
            this.age=age;
            return this;
        }

        public UserBuilder address(String address){
            this.address=address;
            return this;
        }

        public UserBuilder phone(String phone){
            this.phone=phone;
            return this;
        }

        public User build(){
            return new User(this);
        }
    }
}

new User.UserBuilder("Jack","10086")
                .age(25)
                .address("GuangZhou")
                .phone("13800138000")
                .build();

public User build() {
  User user = new user(this);
  if (user.getAge() > 120) {
    throw new IllegalStateException(“Age out of range”); // 线程安全
  }
  return user;
}