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啥叫建造者模式？

就是说需要搞的这个玩意儿比较复杂，您要是一趟车就要搞定，貌似难度比较大。那咋办，你得像建大楼一样，一层层往上盖才行。或者说你得先从小零件搞起，然后慢慢组装，最后成为成品。

举个例子：假如你要生产一台计算机（假设你有能力生产所有部件），那你得先搞个CPU吧，然后再得搞个主板吧（主板上你得搞这种芯片吧），然后你觉得显示效果不爽，你还得搞个显卡吧，然后电源啦，硬盘啦，机箱啦，显示器啦等等等等，折腾了这么多，你搞出一台计算机来。

再比如某机构要登记信息系统的用户信息，一个用户，首先有姓名，年龄，电话，地址，身份证号码，然后名族，是否已婚，学历，家里几口人，种了几亩田，名下有几套房产…吧啦吧啦…等等相关信息，组装起来就是用户。

拼装好了，最后“啪”贴个封条（就是Build方法），就可以出货啦！

貌似看出点意思了，一句话，拼装呗！这时候建造者模式的作用就来了，下面就是代码示例：

package com.creational.builder;public class User {
       //All final attributes    private final String firstName; // required    private final String lastName; // required    private final int age; // optional    private final String phone; // optional    private final String address; // optional    private User(UserBuilder builder) {        this.firstName = builder.firstName;        this.lastName = builder.lastName;        this.age = builder.age;        this.phone = builder.phone;        this.address = builder.address;    }    //All getter, and NO setter to provde immutability    public String getFirstName() {        return firstName;    }    public String getLastName() {        return lastName;    }    public int getAge() {        return age;    }    public String getPhone() {        return phone;    }    public String getAddress() {        return address;    }    @Override    public String toString() {        return "User: "+this.firstName+", "+this.lastName+", "+this.age+", "+this.phone+", "+this.address;    }    public static class UserBuilder     {
           private final String firstName;        private final String lastName;        private int age;        private String phone;        private String address;        public UserBuilder(String firstName, String lastName) {            this.firstName = firstName;            this.lastName = lastName;        }        public UserBuilder age(int age) {            this.age = age;            return this;        }        public UserBuilder phone(String phone) {            this.phone = phone;            return this;        }        public UserBuilder address(String address) {            this.address = address;            return this;        }        //Return the finally consrcuted User object        public User build() {            User user =  new User(this);            validateUserObject(user);            return user;        }        private void validateUserObject(User user) {            //Do some basic validations to check             //if user object does not break any assumption of system            /*if(user.age <= 0){                throw new IllegalArgumentException();            }*/        }    }}

package com.creational.builder;public class TestUserBuilder {    public static void main(String[] args) {        User user1 = new User.UserBuilder("Lokesh", "Gupta")        .age(30)        .phone("1234567")        .address("Fake address 1234")        .build();        System.out.println(user1);        User user2 = new User.UserBuilder("Jack", "Reacher")        .age(40)        .phone("5655")        //no address        .build();        System.out.println(user2);        User user3 = new User.UserBuilder("Super", "Man")        //No age        //No phone        //no address        .build();        System.out.println(user3);    }}

以上代码很好懂，就不用多解释了，最后还是来张建造者的UML来调节一下：

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