Builder模式

模式动机

无论是在现实世界中还是在软件系统中，都存在一些复杂的对象，它们拥有多个组成部分，如汽车，它包括车轮、方向盘、发动机等各种部件。而对于大多数用户而言，无须知道这些部件的装配细节，也几乎不会使用单独某个部件，而是使用一辆完整的汽车，可以通过建造者模式对其进行设计与描述，建造者模式可以将部件和其组装过程分开，一步一步创建一个复杂的对象。用户只需要指定复杂对象的类型就可以得到该对象，而无须知道其内部的具体构造细节。

在软件开发中，也存在大量类似汽车一样的复杂对象，它们拥有一系列成员属性，这些成员属性中有些是引用类型的成员对象。而且在这些复杂对象中，还可能存在一些限制条件，如某些属性没有赋值则复杂对象不能作为一个完整的产品使用；有些属性的赋值必须按照某个顺序，一个属性没有赋值之前，另一个属性可能无法赋值等。

复杂对象相当于一辆有待建造的汽车，而对象的属性相当于汽车的部件，建造产品的过程就相当于组合部件的过程。由于组合部件的过程很复杂，因此，这些部件的组合过程往往被“外部化”到一个称作建造者的对象里，建造者返还给客户端的是一个已经建造完毕的完整产品对象，而用户无须关心该对象所包含的属性以及它们的组装方式，这就是建造者模式的模式动机。

package com.ricky.builder.ch1;

/**
 * ${DESCRIPTION}
 *
 * @author Ricky Fung
 * @create 2016-07-06 16:39
 */
public class Person {
    private final String firstName;
    private final String lastName;
    private final String middleName;
    private final int age;
    private final String street;
    private final String district;
    private final String city;
    private final String province;
    private final boolean isFemale;
    private final boolean isEmployed;

    public Person(String firstName, String lastName, String middleName, int age, String street,
                  String district, String city, String province, boolean isFemale, boolean isEmployed) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.middleName = middleName;
        this.age = age;
        this.street = street;
        this.district = district;
        this.city = city;
        this.province = province;
        this.isFemale = isFemale;
        this.isEmployed = isEmployed;
    }

    @Override
    public String toString() {
        return "Person{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", middleName='" + middleName + '\'' +
                ", age=" + age +
                ", street='" + street + '\'' +
                ", district='" + district + '\'' +
                ", city='" + city + '\'' +
                ", province='" + province + '\'' +
                ", isFemale=" + isFemale +
                ", isEmployed=" + isEmployed +
                '}';
    }
}

package com.ricky.builder.ch1;

/**
 * ${DESCRIPTION}
 *
 * @author Ricky Fung
 * @create 2016-07-06 16:40
 */
public class PersonBuilder {
    private String firstName;
    private String lastName;
    private String middleName;
    private int age;
    private String street;
    private String district;
    private String city;
    private String province;
    private boolean isFemale;
    private boolean isEmployed;

    public PersonBuilder(){
    }

    public PersonBuilder firstName(String firstName) {
        this.firstName = firstName;
        return this;
    }

    public PersonBuilder lastName(String lastName) {
        this.lastName = lastName;
        return this;
    }

    public PersonBuilder middleName(String middleName) {
        this.middleName = middleName;
        return this;
    }
    public PersonBuilder age(int age) {
        this.age = age;
        return this;
    }
    public PersonBuilder street(String street) {
        this.street = street;
        return this;
    }

    public PersonBuilder district(String district) {
        this.district = district;
        return this;
    }

    public PersonBuilder city(String city) {
        this.city = city;
        return this;
    }

    public PersonBuilder province(String province) {
        this.province = province;
        return this;
    }

    public PersonBuilder isFemale(boolean isFemale) {
        this.isFemale = isFemale;
        return this;
    }

    public PersonBuilder isEmployed(boolean isEmployed) {
        this.isEmployed = isEmployed;
        return this;
    }

    public Person create() {

        return new Person(firstName, lastName, middleName, age, street, district, city, province, isFemale, isEmployed);
    }
}

package com.ricky.builder;

import com.ricky.builder.ch1.Person;
import com.ricky.builder.ch1.PersonBuilder;

/**
 * ${DESCRIPTION}
 *
 * @author Ricky Fung
 * @create 2016-07-06 16:41
 */
public class PersonBuilderDemo {

    public static void main(String[] args){

        Person person = new PersonBuilder()
                .firstName("ricky")
                .lastName("fung")
                .age(27)
                .street("建国路")
                .district("朝阳")
                .city("北京市")
                .province("北京")
                .isFemale(false)
                .isEmployed(true)
                .create();

        System.out.println(person);
    }
}