什么时候在对象中使用工厂方法而不是factory类是一个好主意?
当前回答
UML从
Product:它定义Factory方法创建的对象的接口。
ConcreteProduct:实现Product接口
创建者:声明Factory方法
ConcreateCreator:实现Factory方法以返回ConcreteProduct的实例
问题陈述:使用定义游戏界面的工厂方法创建游戏工厂。
代码片段:
import java.util.HashMap;
/* Product interface as per UML diagram */
interface Game{
/* createGame is a complex method, which executes a sequence of game steps */
public void createGame();
}
/* ConcreteProduct implementation as per UML diagram */
class Chess implements Game{
public Chess(){
}
public void createGame(){
System.out.println("---------------------------------------");
System.out.println("Create Chess game");
System.out.println("Opponents:2");
System.out.println("Define 64 blocks");
System.out.println("Place 16 pieces for White opponent");
System.out.println("Place 16 pieces for Black opponent");
System.out.println("Start Chess game");
System.out.println("---------------------------------------");
}
}
class Checkers implements Game{
public Checkers(){
}
public void createGame(){
System.out.println("---------------------------------------");
System.out.println("Create Checkers game");
System.out.println("Opponents:2 or 3 or 4 or 6");
System.out.println("For each opponent, place 10 coins");
System.out.println("Start Checkers game");
System.out.println("---------------------------------------");
}
}
class Ludo implements Game{
public Ludo(){
}
public void createGame(){
System.out.println("---------------------------------------");
System.out.println("Create Ludo game");
System.out.println("Opponents:2 or 3 or 4");
System.out.println("For each opponent, place 4 coins");
System.out.println("Create two dices with numbers from 1-6");
System.out.println("Start Ludo game");
System.out.println("---------------------------------------");
}
}
/* Creator interface as per UML diagram */
interface IGameFactory {
public Game getGame(String gameName);
}
/* ConcreteCreator implementation as per UML diagram */
class GameFactory implements IGameFactory {
HashMap<String,Game> games = new HashMap<String,Game>();
/*
Since Game Creation is complex process, we don't want to create game using new operator every time.
Instead we create Game only once and store it in Factory. When client request a specific game,
Game object is returned from Factory instead of creating new Game on the fly, which is time consuming
*/
public GameFactory(){
games.put(Chess.class.getName(),new Chess());
games.put(Checkers.class.getName(),new Checkers());
games.put(Ludo.class.getName(),new Ludo());
}
public Game getGame(String gameName){
return games.get(gameName);
}
}
public class NonStaticFactoryDemo{
public static void main(String args[]){
if ( args.length < 1){
System.out.println("Usage: java FactoryDemo gameName");
return;
}
GameFactory factory = new GameFactory();
Game game = factory.getGame(args[0]);
if ( game != null ){
game.createGame();
System.out.println("Game="+game.getClass().getName());
}else{
System.out.println(args[0]+ " Game does not exists in factory");
}
}
}
输出:
java NonStaticFactoryDemo Chess
---------------------------------------
Create Chess game
Opponents:2
Define 64 blocks
Place 16 pieces for White opponent
Place 16 pieces for Black opponent
Start Chess game
---------------------------------------
Game=Chess
这个例子通过实现FactoryMethod展示了一个Factory类。
Game is the interface for all type of games. It defines complex method: createGame() Chess, Ludo, Checkers are different variants of games, which provide implementation to createGame() public Game getGame(String gameName) is FactoryMethod in IGameFactory class GameFactory pre-creates different type of games in constructor. It implements IGameFactory factory method. game Name is passed as command line argument to NotStaticFactoryDemo getGame in GameFactory accepts a game name and returns corresponding Game object.
工厂:
创建对象而不向客户端公开实例化逻辑。
FactoryMethod
定义一个用于创建对象的接口，但是让子类来决定实例化哪个类。Factory方法允许类延迟实例化到子类
用例:
何时使用:客户端不知道在运行时需要创建什么具体的类，而只是想获得一个可以完成这项工作的类。
其他回答
我简短的解释是，当我们没有足够的信息来创建一个具体的对象时，我们使用工厂模式。我们要么不知道依赖关系，要么不知道对象的类型。我们几乎总是不知道它们因为这是运行时的信息。
示例:我们知道我们必须创建一个车辆对象，但我们不知道它是飞行还是在地面上工作。
我把工厂比作图书馆的概念。例如，您可以有一个库用于处理数字，另一个库用于处理形状。您可以将这些库的函数存储在逻辑上命名为Numbers或Shapes的目录中。这些是泛型类型，可以包括整数，浮点数，双元，长或矩形，圆形，三角形，在形状的情况下，五边形。
该系统采用了多态、依赖注入和控制反转等技术。
Factory Patterns的目的是:定义一个用于创建对象的接口，但是让子类来决定实例化哪个类。工厂方法允许类延迟实例化到子类。
假设你正在构建一个操作系统或框架，你正在构建所有的离散组件。
下面是PHP中工厂模式概念的一个简单示例。我可能不会完全理解，但这只是一个简单的例子。我不是专家。
class NumbersFactory {
public static function makeNumber( $type, $number ) {
$numObject = null;
$number = null;
switch( $type ) {
case 'float':
$numObject = new Float( $number );
break;
case 'integer':
$numObject = new Integer( $number );
break;
case 'short':
$numObject = new Short( $number );
break;
case 'double':
$numObject = new Double( $number );
break;
case 'long':
$numObject = new Long( $number );
break;
default:
$numObject = new Integer( $number );
break;
}
return $numObject;
}
}
/* Numbers interface */
abstract class Number {
protected $number;
public function __construct( $number ) {
$this->number = $number;
}
abstract public function add();
abstract public function subtract();
abstract public function multiply();
abstract public function divide();
}
/* Float Implementation */
class Float extends Number {
public function add() {
// implementation goes here
}
public function subtract() {
// implementation goes here
}
public function multiply() {
// implementation goes here
}
public function divide() {
// implementation goes here
}
}
/* Integer Implementation */
class Integer extends Number {
public function add() {
// implementation goes here
}
public function subtract() {
// implementation goes here
}
public function multiply() {
// implementation goes here
}
public function divide() {
// implementation goes here
}
}
/* Short Implementation */
class Short extends Number {
public function add() {
// implementation goes here
}
public function subtract() {
// implementation goes here
}
public function multiply() {
// implementation goes here
}
public function divide() {
// implementation goes here
}
}
/* Double Implementation */
class Double extends Number {
public function add() {
// implementation goes here
}
public function subtract() {
// implementation goes here
}
public function multiply() {
// implementation goes here
}
public function divide() {
// implementation goes here
}
}
/* Long Implementation */
class Long extends Number {
public function add() {
// implementation goes here
}
public function subtract() {
// implementation goes here
}
public function multiply() {
// implementation goes here
}
public function divide() {
// implementation goes here
}
}
$number = NumbersFactory::makeNumber( 'float', 12.5 );
清楚地区分使用工厂或工厂方法背后的思想是很重要的。 两者都旨在解决互斥的不同类型的对象创建问题。
让我们具体谈谈“工厂方法”:
首先，当您正在开发库或api时，这些库或api将用于进一步的应用程序开发，那么工厂方法是创建模式的最佳选择之一。原因;我们知道什么时候创建一个所需功能的对象，但对象的类型仍未确定，或者将根据传递的动态参数来决定。
Now the point is, approximately same can be achieved by using factory pattern itself but one huge drawback will introduce into the system if factory pattern will be used for above highlighted problem, it is that your logic of crating different objects(sub classes objects) will be specific to some business condition so in future when you need to extend your library's functionality for other platforms(In more technically, you need to add more sub classes of basic interface or abstract class so factory will return those objects also in addition to existing one based on some dynamic parameters) then every time you need to change(extend) the logic of factory class which will be costly operation and not good from design perspective. On the other side, if "factory method" pattern will be used to perform the same thing then you just need to create additional functionality(sub classes) and get it registered dynamically by injection which doesn't require changes in your base code.
interface Deliverable
{
/*********/
}
abstract class DefaultProducer
{
public void taskToBeDone()
{
Deliverable deliverable = factoryMethodPattern();
}
protected abstract Deliverable factoryMethodPattern();
}
class SpecificDeliverable implements Deliverable
{
/***SPECIFIC TASK CAN BE WRITTEN HERE***/
}
class SpecificProducer extends DefaultProducer
{
protected Deliverable factoryMethodPattern()
{
return new SpecificDeliverable();
}
}
public class MasterApplicationProgram
{
public static void main(String arg[])
{
DefaultProducer defaultProducer = new SpecificProducer();
defaultProducer.taskToBeDone();
}
}
工厂方法应该被认为是构造函数的替代品——尤其是在构造函数表达能力不够的时候。
class Foo{
public Foo(bool withBar);
}
表现力不如:
class Foo{
public static Foo withBar();
public static Foo withoutBar();
}
当你需要一个复杂的过程来构造对象时，当构造需要一个你不想要的实际类的依赖关系时，当你需要构造不同的对象时，工厂类是有用的。
如果你想在使用方面创建一个不同的对象。它很有用。
public class factoryMethodPattern {
static String planName = "COMMERCIALPLAN";
static int units = 3;
public static void main(String args[]) {
GetPlanFactory planFactory = new GetPlanFactory();
Plan p = planFactory.getPlan(planName);
System.out.print("Bill amount for " + planName + " of " + units
+ " units is: ");
p.getRate();
p.calculateBill(units);
}
}
abstract class Plan {
protected double rate;
abstract void getRate();
public void calculateBill(int units) {
System.out.println(units * rate);
}
}
class DomesticPlan extends Plan {
// @override
public void getRate() {
rate = 3.50;
}
}
class CommercialPlan extends Plan {
// @override
public void getRate() {
rate = 7.50;
}
}
class InstitutionalPlan extends Plan {
// @override
public void getRate() {
rate = 5.50;
}
}
class GetPlanFactory {
// use getPlan method to get object of type Plan
public Plan getPlan(String planType) {
if (planType == null) {
return null;
}
if (planType.equalsIgnoreCase("DOMESTICPLAN")) {
return new DomesticPlan();
} else if (planType.equalsIgnoreCase("COMMERCIALPLAN")) {
return new CommercialPlan();
} else if (planType.equalsIgnoreCase("INSTITUTIONALPLAN")) {
return new InstitutionalPlan();
}
return null;
}
}
