用模式替换 if else 语句 [英] Replacing if else statement with pattern

问题描述

我有一个 if else 语句，它可能会在不久的将来增长.

I have a if else statement which might grow in the near future.

    public void decide(String someCondition){

        if(someCondition.equals("conditionOne")){
            //
            someMethod("someParameter");

        }else if(someCondition.equals("conditionTwo")){

           //
           someMethod("anotherParameter");

        }
        .
        .
        else{

            someMethod("elseParameter");

        }
}

既然这看起来已经很乱了，我想如果我能在这里应用任何设计模式会更好.我研究了策略模式，但我不确定这是否会减少这里的其他条件.有什么建议吗?

Since, this is already looking messy, I think it would be better if I can apply any design patterns here. I looked into Strategy pattern but I am not sure if that will reduce if else condition here. Any suggestions?

推荐答案

这是一个经典的Replace Condition使用命令的调度器在重构为模式一书中.

This is a classic Replace Condition dispatcher with Command in the Refactoring to Patterns book.

基本上，您为旧的 if/else 组中的每个代码块创建一个 Command 对象，然后为这些命令创建一个 Map，其中键是您的条件字符串

Basically you make a Command object for each of the blocks of code in your old if/else group and then make a Map of those commands where the keys are your condition Strings

interface Handler{
    void handle( myObject o);
}


 Map<String, Handler> commandMap = new HashMap<>();
 //feel free to factor these out to their own class or
 //if using Java 8 use the new Lambda syntax
 commandMap.put("conditionOne", new Handler(){
         void handle(MyObject o){
                //get desired parameters from MyObject and do stuff
          }
 });
 ...

然后代替您的 if/else 代码:

Then instead of your if/else code it is instead:

 commandMap.get(someCondition).handle(this);

现在，如果您以后需要添加新命令，只需添加到哈希中即可.

Now if you need to later add new commands, you just add to the hash.

如果您想处理默认情况，您可以使用 Null Object 模式来处理条件不在 Map 中的情况.

If you want to handle a default case, you can use the Null Object pattern to handle the case where a condition isn't in the Map.

 Handler defaultHandler = ...

if(commandMap.containsKey(someCondition)){
    commandMap.get(someCondition).handle(this);
}else{
    defaultHandler.handle(this);
}

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