Java map string to function

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

Couldn’t you do String to Method ? Then you can cache the methods you need to execute.

Solution 2

There aren’t any first-class standalone functions, but you can do what you want with an interface. Create an interface that represents your function. For example, you might have the following:

public interface ComputeString

Then you can create a Map object like you want in the first place. Using a map will be much faster than reflection and will also give more type-safety, so I would advise the above.

Solution 3

While you can’t have first class functions, there are anonymous classes which can be based on an interface:

interface ProcessingMethod < String method(); >Map methodMap = new HashMap(); methodMap.put("abc", new ProcessingMethod() < String method() < return "xyz" >>); methodMap.put("def", new ProcessingMethod() < String method() < return "uvw" >>); methodMap.get("abc").method(); 

Solution 4

This example uses an enum of named functions and an abstract FunctionAdapter to invoke functions with a variable number of homogeneous parameters without reflection. The lookup() function simply uses Enum.valueOf , but a Map might be worth it for a large number of functions.

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Comments

Currently, I have a bunch of Java classes that implement a Processor interface, meaning they all have a processRequest(String key) method. The idea is that each class has a few (say, <10) member Strings , and each of those maps to a method in that class via the processRequest method, like so:

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. > 

• 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.
• This seems WAY slower than the if-else 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.

TL; DR: I’m looking for a clean, minimal-overhead way to map a String to some sort of a Function object that I can invoke and call (something like) getReturnType() on. I don’t especially mind using a 3rd-party library if it really 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 Map with reflection.

Thoughts on a good way to get what I want? Cheers!

Couldn’t you do String to Method (java.sun.com/j2se/1.4.2/docs/api/java/lang/reflect/Method.h‌​tml)? Then you can cache the methods you need to execute.

That would mean having an implementing class for every single function I want to invoke, which seems clunky and requires a bit of boilerplate for every single function. Doesn’t sound that awesome to me.

@Bears, yeah it is clunky, but you can construct anonymous classes, which should make it somewhat less clunky, like map.put(str,new ComputeString()>);

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Java map string to function

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