1 概述
建造者模式(Builder Pattern)主要用于“分步骤构建一个复杂的对象”,在这其中“分步骤”是一个稳定的算法,而复杂对象的各个部分则经常变化。因此, 建造者模式主要用来解决“对象部分”的需求变化。 这样可以对对象构造的过程进行更加精细的控制。
2 示例
以生产手机为例,每个手机分为屏幕Screen、CPU、Battery。现在要生产两种手机,苹果机和三星。
苹果:
package org.scott.builder.before.use;
import java.util.ArrayList;
import java.util.List;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public class ApplePhone {
List<String> parts = new ArrayList<String>();
public void createCPU() {
parts.add("CUP: Qualcomm");
}
public void createScreen() {
parts.add("SCREEN: JDI");
}
public void createBattery() {
parts.add("BATTERY: DeSai");
}
public void show(){
System.out.print("产品部件信息:");
for(String part : parts){
System.out.print(part + "\t");
}
}
}
三星:
package org.scott.builder.before.use;
import java.util.ArrayList;
import java.util.List;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public class SamsungPhone {
List<String> parts = new ArrayList<String>();
public void createCPU() {
parts.add("CUP: MTK");
}
public void createScreen() {
parts.add("SCREEN: Samsung");
}
public void createBattery() {
parts.add("BATTERY: DeSai");
}
public void show(){
System.out.print("产品部件信息:");
for(String part : parts){
System.out.print(part + "\t");
}
}
}
测试客户端:
package org.scott.builder.before.use;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public class BuilerTest {
private static ApplePhone iphone = new ApplePhone();
private static SamsungPhone samPhone = new SamsungPhone();
public static void main(String args[]){
iphone.createCPU();
iphone.createScreen();
iphone.createBattery();
iphone.show();
samPhone.createCPU();
samPhone.createScreen();
samPhone.createBattery();
samPhone.show();
}
}
是不是发现个问题?那就是生产手机的每一道工序都是一样的,确切的说是工序名称一样,只是具体的每个工序的处理不同,工序是不变的,就这么几步,每道工序的具体处理是变化的,由此,我们可以把不变的抽取出来,以“不变应万变”,将变化的,交给具体的产品来做。
具体怎么做?这回的Builder模式派上用场了。
首先来个Phone的接口:
package org.scott.builder.after.use;
import java.util.ArrayList;
import java.util.List;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public abstract class Phone {
protected List<String> parts = new ArrayList<String>();
public void add(String part){
parts.add(part);
}
public void show(){
System.out.print("产品部件信息:");
for(String part : parts){
System.out.print(part + "\t");
}
}
}
苹果手机类:
package org.scott.builder.after.use;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public class ApplePhone extends Phone{
}
三星手机类:
package org.scott.builder.after.use;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public class SamsungPhone extends Phone{
}
再定义个生产步骤的接口Builder:
package org.scott.builder.after.use;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public interface Builder {
public void buildCPU();
public void buildScreen();
public void buildBattery();
public Phone getPhone();
}
苹果手机的Builder:
package org.scott.builder.after.use;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public class ApplePhoneBuilder implements Builder{
private Phone phone = new ApplePhone();
@Override
public void buildCPU() {
phone.add("CUP: Qualcomm");
}
@Override
public void buildScreen() {
phone.add("SCREEN: JDI");
}
@Override
public void buildBattery() {
phone.add("BATTERY: DeSai");
}
@Override
public Phone getPhone() {
return phone;
}
}
三星手机的Builder:
package org.scott.builder.after.use;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public class SamsungPhoneBuilder implements Builder{
private Phone phone = new SamsungPhone();
@Override
public void buildCPU() {
phone.add("CUP: MTK");
}
@Override
public void buildScreen() {
phone.add("SCREEN: Samsung");
}
@Override
public void buildBattery() {
phone.add("BATTERY: DeSai");
}
@Override
public Phone getPhone() {
return phone;
}
}
指导具体生产手机的Director:
package org.scott.builder.after.use;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public class Director {
private Builder builder;
public Director(Builder builder){
this.builder = builder;
}
public void construct(){
builder.buildCPU();
builder.buildScreen();
builder.buildBattery();
}
}
最后写个测试类:
package org.scott.builder.after.use;
/**
* @author Scott
* @version 2013-11-20
* @description
*/
public class BuilderTest {
private static Builder iPhoneBuilder = new ApplePhoneBuilder();
private static Builder samPhoneBuilder = new SamsungPhoneBuilder();
public static void main(String[] args) {
Director director = new Director(iPhoneBuilder);
director.construct();
Phone phone = iPhoneBuilder.getPhone();
System.out.println("iphone");
phone.show();
director = new Director(samPhoneBuilder);
director.construct();
phone = samPhoneBuilder.getPhone();
System.out.println("\nsamSung");
phone.show();
}
}
运行结果:
iphone
产品部件信息:CUP: Qualcomm SCREEN: JDI BATTERY: DeSai
samSung
产品部件信息:CUP: MTK SCREEN: Samsung BATTERY: DeSai
这里的两个Phone实体类是空的,如果是这种情况,那么它们可以省略掉,如果 Phone接口也可以被省略掉,最终剩下的就只有 Director、Builder、和具体的 Bulider 实现类。并且,ApplePhone类和 SamsungPhone类是有关系的两个类,它们不同的手机品牌,如果遇到两个或多个没有太多关系的类,公共的接口Phone就没有存在的必要,但是这时候,那么 Builder 接口的规定的 getPhone() 方法的返回值怎么确定呢?
无论返回值类型是 ApplePhone还是SamsungPhone,都会产生问题,因为返回结果的类型不统一。此时,可以将 Phone定义成一个空接口(不包含任何方法的接口),再让这些没有相互关系的具体产品类都去实现这个接口,那么 Builder 接口里面规定的 getPhone() 方法的返回值类型依然是 Phone 类型,就解决问题了。不过这种情况下,也就没有使用Builder模式的必要了。