23种设计模式

1、策略枚举
2、责任链模式

1、策略枚举

• 使用策略枚举消除大量使用的if else

• 使用大量 if-else

public class IfService {public String getToDo(String day) {if ("Monday".equals(day)) {return "今天上英语课";} else if ("Tuesday".equals(day)) {return "今天上语文课";} else if ("Wednesday".equals(day)) {return "今天上数学课";} else if ("Thursday".equals(day)) {return "今天上音乐课";} else if ("sunday".equals(day)) {return "今天上编程课";} else {return null;}}public static void main(String[] args) {IfService ifService = new IfService();System.out.println(ifService.getToDo("Monday"));}
}

结果：

• 使用枚举类进行优化大量if -else

public class CheckDay {public String day(DayEnum dayEnum){return  dayEnum.toDo();}}

public enum DayEnum {Monday{@Overridepublic String toDo(){return "周一";}},Tuesday{@Overridepublic String toDo(){return "周二";}},Wendsday{@Overridepublic String toDo(){return "周三";}},Thursday{@Overridepublic String toDo(){return "周四";}},Friday{@Overridepublic String toDo(){return "周五";}};public abstract String toDo();
}

    public static void main(String[] args) {CheckDay checkDay = new CheckDay();//可以传递参数选择哪个 枚举对象String monday = checkDay.day(DayEnum.valueOf("Monday"));System.out.println(monday);}
}

• 另一种情况

    public String getToDo(String day) {//第一种情况
//        if ("Monday".equals(day)) {
//            return "今天上英语课";
//        } else if ("Tuesday".equals(day)) {
//            return "今天上语文课";
//        } else if ("Wednesday".equals(day)) {
//            return "今天上数学课";
//        } else if ("Thursday".equals(day)) {
//            return "今天上音乐课";
//        } else if ("sunday".equals(day)) {
//            return "今天上编程课";
//        } else {
//            return null;
//        }//第二种情况if("Monday".equals(day)||"Tuesday".equals(day)||"Wednesday".equals(day)){return "今天上英语课";}else if("Thursday".equals(day)){return null;}return null;}

public class CheckDay {public String dayNew(DayEnumNew dayEnumNew) {return dayEnumNew.toDo();}
}

public enum DayEnumNew {Monday(Type.ENGLISH, "星期一"),Tuesday(Type.ENGLISH, "星期二"),Wednesday(Type.ENGLISH, "星期三"),Thursday(Type.CHINESE, "星期四");private final Type type;private final String day;DayEnumNew(Type type, String day) {this.type = type;this.day = day;}String toDo(){return type.toDo();}/*** 内部策略枚举*/private enum Type {ENGLISH {@Overridepublic String toDo() {return "今天上英语课";}},CHINESE {@Overridepublic String toDo() {return "今天上语文课";}};public abstract String toDo();}
}

    public static void main(String[] args) {CheckDay checkDay = new CheckDay();//可以传递参数选择哪个 枚举对象
//        String monday = checkDay.day(DayEnum.valueOf("Monday"));
//        System.out.println(monday);String monday = checkDay.dayNew(DayEnumNew.valueOf("Monday"));String thursday = checkDay.dayNew(DayEnumNew.valueOf("Thursday"));String thursday1 = checkDay.dayNew(DayEnumNew.valueOf("Wednesday"));System.out.println(monday);System.out.println(thursday);System.out.println(thursday1);}

结果：

2、责任链模式

用『责任链模式』来优化 参数多重校验，非常优雅！
以前在做需求，写一个方法，先在前面做验证，
if不满足A条件则return，
if不满足B条件则return…
一共写了5个验证，等验证通过以后才执行下面的逻辑，
后来提了需求，跟这个方法类似，
只不过验证条件稍微有点不一样，变成6个验证了

处理器：

public abstract class Handler<T> {protected Handler next;private void next(Handler next) {this.next = next;}public abstract void doHandler(User user);public static class Builder<T> {private Handler<T> head;private Handler<T> tail;public Builder<T> addHandler(Handler handler) {if (this.head == null) {this.head = this.tail = handler;return this;}this.tail.next(handler);this.tail = handler;return this;}public Handler<T> build() {return this.head;}}
}

@Data
public class User {private String userName;private String passWord;private String roleName;
}

进行校验：

public class LoginHandler  extends  Handler{@Overridepublic void doHandler(User user) {if (!"GJ".equals(user.getUserName()) && !"123456".equals(user.getPassWord())){System.out.println("用户名或密码错误!");
//            return;}//判断是否还有下一个处理器，如果有则继续处理if (null!=next){next.doHandler(user);}}
}

public class AuthHandler extends  Handler{@Overridepublic void doHandler(User user) {if (!"管理员".equals(user.getRoleName())){System.out.println("不是管理员，不允许访问");
//            return;}if (next != null){next.doHandler(user);}}
}

public class LogicHandler  extends  Handler {@Overridepublic void doHandler(User user) {System.out.println("逻辑处理");if (next != null){next.doHandler(user);}}}

测试方法

public class Test {public static void main(String[] args) {Handler.Builder builder = new Handler.Builder<>();builder.addHandler(new LoginHandler()).addHandler(new AuthHandler()).addHandler(new LogicHandler());User user = new User();user.setUserName("GJ");user.setPassWord("123456");user.setRoleName("普通用户");builder.build().doHandler(user);}
}

结果：