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POHow can I map a String to a function in Java?
 

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  1. POHow can I map a String to a function in Java?
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    <p>Currently, I have a bunch of Java classes that implement a <code>Processor</code> interface, meaning they all have a <code>processRequest(String key)</code> method. The idea is that each class has a few (say, &lt;10) member <code>Strings</code>, and each of those maps to a method in that class via the <code>processRequest</code> method, like so:</p> <pre><code>class FooProcessor implements Processor { String key1 = "abc"; String key2 = "def"; String key3 = "ghi"; // and so on... String processRequest(String key) { String toReturn = null; if (key1.equals(key)) toReturn = method1(); else if (key2.equals(key)) toReturn = method2(); else if (key3.equals(key)) toReturn = method3(); // and so on... return toReturn; } String method1() { // do stuff } String method2() { // do other stuff } String method3() { // do other other stuff } // and so on... } </code></pre> <p>You get the idea.</p> <p>This was working fine for me, but now I need a runtime-accessible mapping from key to function; not every function <em>actually</em> returns a String (some return void) and I need to dynamically access the return type (using reflection) of each function in each class that there's a key for. I already have a manager that knows about all the keys, but <em>not</em> the mapping from key to function.</p> <p>My first instinct was to replace this mapping using <code>if-else</code> statements with a <code>Map&lt;String, Function&gt;</code>, like I could do in Javascript. But, Java doesn't support first-class functions so I'm out of luck there. I could probably dig up a third-party library that lets me work with first-class functions, but I haven't seen any yet, and I doubt that I need an entire new library.</p> <p>I also thought of putting these <code>String</code> keys into an array and using reflection to invoke the methods by name, but I see two downsides to this method:</p> <ul> <li>My keys would have to be named the same as the method - or be named in a particular, consistent way so that it's easy to map them to the method name.</li> <li>This seems WAY slower than the <code>if-else</code> statements I have right now. Efficiency is something of a concern because these methods will tend to get called pretty frequently, and I want to minimize unnecessary overhead.</li> </ul> <hr> <p><strong>TL; DR:</strong> I'm looking for a clean, minimal-overhead way to map a <code>String</code> to some sort of a <code>Function</code> object that I can invoke and call (something like) <code>getReturnType()</code> on. I don't especially mind using a 3rd-party library if it <em>really</em> fits my needs. I also don't mind using reflection, though I would strongly prefer to avoid using reflection every single time I do a method lookup - maybe using some caching strategy that combines the <code>Map</code> with reflection.</p> <p>Thoughts on a good way to get what I want? Cheers!</p>
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    1. USMatt Ball
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    1. COCouldn't you do String to Method (http://java.sun.com/j2se/1.4.2/docs/api/java/lang/reflect/Method.html)? Then you can cache the methods you need to execute.
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      1. POHow can I map a String to a function in Java?
      1. USChris Dennett
    2. CO@Chris - yeah, that's basically where I was heading at the end of my question.
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    3. CODone it :) :) :)
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