使用面向对象技术替代switch.docx
使用面对对象技术替代switch-case和if-else在日常开发中，经常会作一些状态推断，用到swich-case与if-else。在面对对象的环境里，有两种方式可以替代它们。一种是使用继承子类的多态，另一种是使 用state模式。它们使用对象的间接性有效地摆脱了传统的状态推断。举个例子在日常开发中，经常会作一些状态推断，用到swich-case与if-else。在面对对象的环境里，有两种方式可以替代它们。一种是使用继承子类的多态，另一种是使 用state模式。它们使用对象的间接性有效地摆脱了传统的状态推断。举个例子。Method, javapackage ;import ;public class Method private int _type;int POST = 0;public static finalpublic static finalpublic static finalint GET = 1;public static finalint PUT = 2;public static final int DELETE = 3;public Method(int type) _type = type;)public String getMethod() throws NoMethodTypeException switch (_type) case POST: return "This is POST method"case GET:return "This is GET method11;case PUT:return "This is PUT method"case DELETE:return "Thisis DELETE method"default:throw new NoMethodTypeException(); ) )public boolean safeMethod() if (_type = GET) return true;else return false;)public boolean passwordRequired() if (_type = POST)return false;else return true;)类Method中,存在四个状态Post、Get、Put和Delete。有一个switch-case推断, 用于输出四种方法的描述信息；两个if-else推断，分别推断方法是否平安(只有Get方法 是平安的)，方法是否需要密码(只有Post方法不需要密码)o1 .使用继承子类多态使用继承子类多态的方式，通常对于某个详细对象，它的状态是不行转变的(在对象的 生存周期中)。<!一if !vml一><!一endif 一>现在使用四个子类分别代表四种类型的方法。这样就可以使用多态将各个方法的详细规 律分置到子类中去了。在抽象基类Method中可以供应创立子类实例的静态方法，当然也可以使用Simple Factory模式。对于gtMethod ()方法,延迟到子类中实现；对于safMethod ()方法和 passwordRequired ()方法，供应一个默认的实现，这个实现应当符合绝大局部子类的要 求，这样的话，对于少数不符合默认实现的子类只需。verride相应方法即可。<<abstract>Method. java package ;public abstract class Method public final static Method createPostMethod() return new PostMethod();)public final static Method createGetMethod() return new GtMthod();)public final static Mthod cratPutMthod() return new PutMethod();)public final static Method createDeleteMethod() return new DelMethod();)abstract public String getMethod();public boolean safeMethod() return false;)public boolean passwordRequired() return true;)四个子类分别继承和override相应的方法。PostMethod, javapackage ;public class PostMethod extends Method QOverridepublic String getMethod() return "This is POST method")Overridepublic boolean passwordRequired() return false;)GetMethod.javapackage ;public class GetMethod extends MethodOverridepublic String getMethod() return nThis is GET method")Overridepublic boolean safeMethod() return true;)PutMethod.javapackage ;public class PutMethod extends Method Overridepublic String getMethod() return "This is PUT method")DelMethod. javapackage ;public class DelMethod extends MOverridepublic String getMethod() return "This is DELETE method")2.使用state模式假如盼望对象在生存周期内，可以变化自己的状态，那么可以选择state模式。<!一if !vml一>!-endif一这里抽象状态为一个接口 MethodType,四种不同的状态实现该接口。 interfaceMethodType. javapackage ;public interface MethodType String getTypeDescription();String getMethodDescription();boolean isSafe();boolean isRequired();Post, javapackage ;public class Post implements MethodTypepublic String getMthodDscription() return "This is POST method")public String gtTypDescription() return n=POST=n;)public boolean isRequired() return false;)public boolean isSafe () return false;)Get, javapackage ;public class Get implements MthodTyp;public String getMethodDescription() return "This is GET method11;)public String getTypeDescription() return n=GET=n;)public boolean isRequired() return true;)public boolean isSafe () return true;)Put. javapackage ;public class Put implements MethodTypepublic String getMethodDescription() return "This is PUT method")public String getTypeDescription() return n=PUT=n;)public boolean isRequired() return true;)public boolean isSafe () return false;)Delete, javapackage ;public class Delete implements MethodTypepublic String getMethodDescription() return "This is DELETE method")public String gtTypDscription() return n=DELETE=n;)public boolean isRequired() return true;)public boolean isSafe () return false;)此时，在类Method中保存一个field表示MethodType,在某对象中，可以随时变化四 种的状态(详细见runAIlMthods ()方法)。Method, javapackagepublic class Method private MethodType _type;public Method() _type = null;)public Method(MethodType type) _type = type;)public String getMethod() return _type.getMethodDescription(); )public boolean safeMethod() return _type.isSafe();)public boolean passwordRequired() return _type.isRequired();)public void changeType(MethodType type) _typ = type;)public void runAllMethods() MethodType types = new MethodType new Post () , new Get (), new Put(), new Delete() ;for (MethodType type : types) System.out.printin(type.getTypeDescription(); changeType(type);System.out.printin(getMethod();System.out.printin(safeMethod();System, out .printin (passwordR;quirci (); ) ) ) 3.测试在测试类中，分别使用上面3中机制展现结果。它们的结果应当是全都的。Client, java package ;public class Client static void print (String s) System.out.printin(s);)static void print(Boolean b) System.out.printin(b);)public static void main(String args) throws NoNtethociTypException print(n=original=n);print(n=POST=n);postl = new (com.zj.original.Method.POST);print(postl.gtMthod();print(postl.safeMethod();print(postl.passwordRequired();print(n=GET=");getl = new (com.zj . original.Method.GET);print (getl.getMethod();print (getl.safeMethod();print(getl.passwordRequired();print(n=puT=n);putl = new (com.zj.original.Method.PUT);print(putl, getMethod();print(putl, safeMethod();print(putl.passwordRequired();print(n=DELETE=n);dell = new (com.zj . original.Method.DELETE);print(dell.getMethod();print (dell.safeMethod();print(dell.passwordRequired();print(n=subclass=n);print(n=POST=n );post2 =, createPostMethod();print (post2.getMethod();print(post2.safeMethod();print(post2.passwordRequired();print("=GET=");get2 = com.zj.subclass.Method.createGetMethod();print(get2.getMethod();print(get2.safeMethod();print(get2.passwordRequired();print ( "=PUT=");put2 = com.zj . subclass.Method.createPutMethod();print (put2.getMethod();print (put2.safeMethod();print(put2.passwordRequired();print(n=DELETE=H);de 12 =.createDeleteMethod();print(del2.getMethod();print(de12.safeMethod();print(de12.passwordRequired();print(n=state=n );new (), runAHMethods ();)原文出处：中软卓越htt
