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对象都需要创建,如果创建的时候直接 new
该对象,就会对该对象严重耦合。
假如我们要更换对象,所有 new
对象的地方都需要修改一遍,显然违背了软件设计的开闭原则(OCP)。如果我们使用工厂来生产对象,我们就只和工厂打交道就可以了,彻底和对象解耦,如果要更换对象,直接在工厂里更换该对象即可,达到了与对象解耦的目的。
工厂模式最大的优点就是:解耦。
定义:一个工厂方法,依据传入的参数,生成对应的产品对象;
角色:
使用说明:
public abstract class Fruit {
abstract void getName();
}
具体类 苹果
public class Apple extends Fruit {
@Override
public void getName() {
System.out.println("Apple");
}
}
具体类 梨
public class Pear extends Fruit {
@Override
public void getName() {
System.out.println("Pear");
}
}
水果工厂
public class FruitFactory {
public Fruit createFruit(String type) {
System.out.println("======SimpleFactory======");
if (type.equals("apple")) {// 生产苹果
return new Apple();
} else if (type.equals("pear")) {// 生产梨
return new Pear();
}
return null;
}
}
简单工厂使用
public class SimpleFactory {
public static void main(String[] args) {
FruitFactory Factory = new FruitFactory();
Apple apple = (Apple) Factory.createFruit("apple");// 获得苹果
apple.getName();
Pear pear = (Pear) Factory.createFruit("pear");// 获得梨
pear.getName();
}
}
小结:
定义:将工厂提取成一个接口或抽象类,具体生产什么产品由子类决定。(具体工厂生产具体类)
角色:
水果抽象类 苹果类和梨类 代码和上例一样,此处省略。
抽象工厂类
public abstract class FruitFactory {
public abstract Fruit createFruit();//生产水果
}
具体工厂 苹果工厂
public class AppleFactory extends FruitFactory {
@Override
public Fruit createFruit() {
return new Apple();
}
}
具体工厂 梨工厂
public class PearFactory extends FruitFactory {
@Override
public Fruit createFruit() {
return new Pear();
}
}
工厂方法使用
public class FactoryMethod {
public static void main(String[] args) {
System.out.println("======FactoryMethod======");
AppleFactory appleFactory = new AppleFactory();
PearFactory pearFactory = new PearFactory();
Apple apple = (Apple) appleFactory.createFruit();// 获得苹果
apple.getName();
Pear pear = (Pear) pearFactory.createFruit();// 获得梨
pear.getName();
}
}
小结:
定义:为创建一组相关或者是相互依赖的对象提供的一个接口,而不需要指定它们的具体类。
角色:
抽象工厂和工厂方法的模式基本一样,区别在于,工厂方法是生产一个具体的产品,而抽象工厂可以用来生产一组相同,有相对关系的产品;重点在于一组,一批,一系列。
举个例子,假如生产 Iphone 手机,Iphone 手机有很多系列,Iphone8、IphoneXS等;假如Iphone8生产需要 CPU A11的处理器,LCD屏幕,而 IphoneXS 需要 CPU A12 的处理器和 OLED 屏幕;用抽象工厂来实现:
CPU 抽象类和实现类
public abstract class CPU {
public abstract void run();
}
public class A11 extends CPU {
@Override
public void run() {
System.out.println("A11");
}
}
public class A12 extends CPU {
@Override
public void run() {
System.out.println("A12");
}
}
屏幕 抽象类和实现类
public abstract class Screen {
public abstract void isScreen();
}
public class LCD extends Screen {
@Override
public void isScreen() {
System.out.println("LCD");
}
}
public class OLED extends Screen {
@Override
public void isScreen() {
System.out.println("OLED");
}
}
手机工厂接口
public interface PhoneFactory {
CPU getCpu();// 使用的cpu
Screen getScreen();// 使用的屏幕
}
手机工厂实现
public class Iphone8Factory implements PhoneFactory {
@Override
public CPU getCpu() {
return new A11();
}
@Override
public Screen getScreen() {
return new LCD();
}
}
public class IphoneXsFactory implements PhoneFactory {
@Override
public CPU getCpu() {
return new A12();
}
@Override
public Screen getScreen() {
return new OLED();
}
}
抽象工厂使用
public class AbstractFactory {
public static void main(String[] args) {
Iphone8Factory iphone8Factory = new Iphone8Factory();
IphoneXsFactory iphoneXSFactory = new IphoneXsFactory();
System.out.println("======iphone8Factory=====");
CPU cpuA11 = iphone8Factory.getCpu();
cpuA11.run();
Screen screenLCD = iphone8Factory.getScreen();
screenLCD.isScreen();
System.out.println("======iphoneXsFactory=====");
CPU cpuA12 = iphoneXSFactory.getCpu();
cpuA12.run();
Screen screenOLED = iphoneXSFactory.getScreen();
screenOLED.isScreen();
}
}
小结:
下面是 JDK 的源码:
Calendar.getInstance();
public static Calendar getInstance(){
return createCalendar(TimeZone.getDefault(), Locale.getDefault(Locale.Category.FORMAT));
}
public static Locale getDefault(Locale.Category category) {
// do not synchronize this method - see 4071298
switch (category) {
case DISPLAY:
if (defaultDisplayLocale == null) {
synchronized(Locale.class) {
if (defaultDisplayLocale == null) {
defaultDisplayLocale = initDefault(category);
}
}
}
return defaultDisplayLocale;
case FORMAT:
if (defaultFormatLocale == null) {
synchronized(Locale.class) {
if (defaultFormatLocale == null) {
defaultFormatLocale = initDefault(category);
}
}
}
return defaultFormatLocale;
default:
assert false: "Unknown Category";
}
return getDefault();
}
private static Calendar createCalendar(TimeZone zone,Locale aLocale){
CalendarProvider provider =
LocaleProviderAdapter.getAdapter(CalendarProvider.class, aLocale)
.getCalendarProvider();
if (provider != null) {
try {
return provider.getInstance(zone, aLocale);
} catch (IllegalArgumentException iae) {
// fall back to the default instantiation
}
}
Calendar cal = null;
if (aLocale.hasExtensions()) {
String caltype = aLocale.getUnicodeLocaleType("ca");
if (caltype != null) {
switch (caltype) {
case "buddhist":
cal = new BuddhistCalendar(zone, aLocale);
break;
case "japanese":
cal = new JapaneseImperialCalendar(zone, aLocale);
break;
case "gregory":
cal = new GregorianCalendar(zone, aLocale);
break;
}
}
}
if (cal == null) {
// If no known calendar type is explicitly specified,
// perform the traditional way to create a Calendar:
// create a BuddhistCalendar for th_TH locale,
// a JapaneseImperialCalendar for ja_JP_JP locale, or
// a GregorianCalendar for any other locales.
// NOTE: The language, country and variant strings are interned.
if (aLocale.getLanguage() == "th" && aLocale.getCountry() == "TH") {
cal = new BuddhistCalendar(zone, aLocale);
} else if (aLocale.getVariant() == "JP" && aLocale.getLanguage() == "ja"
&& aLocale.getCountry() == "JP") {
cal = new JapaneseImperialCalendar(zone, aLocale);
} else {
cal = new GregorianCalendar(zone, aLocale);
}
}
return cal;
}