function name as a string

Question

I am trying to wrap my head around generic and functions... what I am trying to achieve: Passing function name as a string to get it executed:

I want to do Wrapper.useFunction("eleven") or Wrapper.useFunction("ten")

public class Wrapper<T> {
    public F useFunction(Function<F, F> function) {
        return function.apply(F);
    }

    Function<F, String> ten = s -> "10";
    Function<F, String> eleven = s -> "11";
}

But this code not even close to compiling. Maybe it doesn't make any sense. Any suggestions?

I saw example with reflections. Isn't there way to do that with java 8 without reflections? — lapkritinis
– lapkritinis, Commented Aug 22, 2017 at 16:33
It would not be wise to waste time trying. Reflection was built for this. — anomeric
– anomeric, Commented Aug 22, 2017 at 16:34
@PutinasPiliponis No. The only way to call function using string with function name, is the use of reflection. — Andreas
– Andreas, Commented Aug 22, 2017 at 16:35
if you don't want to use reflection, you can replace String with your own enum class. for example: wrapper.use(ELEVEN) — holi-java
– holi-java, Commented Aug 22, 2017 at 16:37

DudeDoesThings · Accepted Answer · 2017-08-22 16:42:37Z

If you have a finite set of functions which you would like to be able to call I would recommend building a Map which maps Strings to instances of Runnable (or similar functional interfaces). Your useFunction method may then look up the function implementation in the Map and call it if it exists.

Example:

public class SomeClass {

    private final Map<String, Runnable> methods = new HashMap<>();
    {
        methods.put("helloworld", () -> {
            System.out.println("Hello World!");
        });
        methods.put("test", () -> {
            System.out.println("test!");
        });
        methods.put("doStuff", () -> {
            System.out.println("doStuff!");
        });
    }

    public void perform(String code) {
        methods.getOrDefault(code, 
            () -> {
                System.err.println("No such Method: "+code);
            })
        .run();
    }

}

If you want to call arbitrary methods you should probably use Reflection as stated by others.

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