工厂模式.何时使用工厂方法？

当您需要具有相同参数类型但具有不同行为的多个"构造函数"时,它们也很有用.

在以下情况下使用对象内部的工厂方法是个好主意:

Object的类不知道它必须创建什么确切的子类

Object的类被设计为使其创建的对象由子类指定

Object的类将其职责委托给辅助子类,并且不知道确切的类将承担这些职责

在以下情况下使用抽象工厂类是个好主意:

您的对象不应该依赖于其内部对象的创建和设计方式

应该一起使用一组链接对象,您需要提供此约束

对象应该由几个可能的链接对象系列之一配置,这些链接对象将成为父对象的一部分

需要共享仅显示接口但不是实现的子对象

UML来自

Product:它定义Factory方法创建的对象的接口.

ConcreteProduct:实现产品界面

创建者:声明工厂方法

ConcreateCreator: 实现Factory方法以返回ConcreteProduct的实例

问题陈述:使用工厂方法创建游戏工厂,工厂方法定义游戏界面.

代码段:

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 games = new HashMap();
    /*  
        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");
        }           
    }
}

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