Question

我正在编写一个协议类，其中包含很多if / elses ......这是类：

public class Protocol {
    Scanner scan = new Scanner(System.in);
    private static final int WAITING = 0;
    private static final int SENTREQUEST = 1;
    private static final int SENTITEMS = 2;
    private static final int ANOTHER = 3;
    private static final int CHOICE = 4;
    private int choice;

    private int state = WAITING;



    public String processInput(String theInput) {
        String theOutput = null;

        if (state == WAITING) {
            theOutput = "Do you accept the terms of agreement? Y/N?";
            state = SENTREQUEST;
        } else if (state == SENTREQUEST) {
            if (theInput.equalsIgnoreCase("y")) {

              theOutput = ": 1. program file 2. pictures 3. documentation";
              state = CHOICE;
             } else {
                theOutput = "Invalid Input!";
                state = SENTITEMS;

            }

        }
        else if (state == CHOICE) {
            choice = scan.nextInt();
            switch(choice) {
                case 1: theOutput = "show something";
                break;
                case 2: theOutput = "show something";
                break;
                case 3: theOutput = "show something";
                break;
            }
        }
        else if (state == SENTITEMS) {

              theOutput = "Want another? (y/n)";
                state = ANOTHER;

        } else if (state == ANOTHER) {

              theOutput = "Do you accept the terms of agreement? Y/N?";

            if (theInput.equalsIgnoreCase("y")) {
                theOutput ="test";
                state = SENTREQUEST;
            } else {
                theOutput = "Bye.";
                state = WAITING;
            }
        }
        return theOutput;
    }
}

它没有进入切换案例，我确定这是一个正确地打破if / elses子句但我找不到问题的问题。

Answer 1

为了解决类似的问题，我将strategy pattern实现为枚举。对于每个策略，您为枚举创建一个新值，在枚举方法中包含代码：

public enum Strategy {

    FIRST_STRATEGY {
        public String process(String input) {
            // Implementation for first strategy
            return null;
        }       
    },

    SECOND_STRATEGY {
        public String process(String input) {
            // Implementation for second strategy
            return null;
        }       

    };

    public abstract String process(String input);

}

您可以根据您拥有的枚举值应用所选策略，实际上删除了if / else语句链：

Strategy chosenStrategy = Strategy.FIRST_STRATEGY;
String output = chosenStrategy.process(input);

这是我为我的一个问题申请的解决方案，也许它不是最优的，也不是面向对象的。您必须为您的问题选择正确的解决方案，但我希望我的经验可以提供帮助。

Answer 2

使用这样的状态模式：

public class Protocol {
    Scanner scan = new Scanner(System.in);

    private abstract class State { abstract String doit(String theInput); }

    private final class WAITING extends State {
      String doit(String theInput) {
         state = SENTREQUEST;
         return "Do you accept the terms of agreement? Y/N?";
      }
    }

    private final class SENTREQUEST extends State {
      String doIt(String theInput) {
        if (theInput.equalsIgnoreCase("y")) {
              state = CHOICE;
              return ": 1. program file 2. pictures 3. documentation";
             } else {
                state = SENTITEMS;
                return "Invalid Input!";
            }
      }
    }

 //TODO refactoring to State classes for all
 //        private static final int SENTITEMS = 2;
 //        private static final int ANOTHER = 3;
 //        private static final int CHOICE = 4;*/
    private int choice;

    private State state = WAITING;



    public String processInput(String theInput) {
        return state.doIt(theInput);
    }
}

帮助突破if / else？

2 个答案: