帮助打破 if/else 吗？

Question

我正在编写一个协议类，其中包含很多 if/elses..这是该类：

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;
    }
}

它没有到达 switch case，并且我确信这是正确突破 if/elses 子句的问题但我找不到问题。

Answer 1

为了解决类似的问题，一旦我将策略模式实现为枚举。对于每个策略，您为枚举创建一个新值，将代码封装在枚举方法中：

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 if/else 语句链：

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

这是我的解决方案应用于我的一个问题，也许它不是最优的或者更面向对象的。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有所帮助。

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);
    }
}