Setting Variable Name from String in Java from User Input

Question

So I've scoured the internet for a fix, and i've gotten tips to use maps, the reflect method, and a ton of other stuff, but nothing has worked the way I wanted.

My goal is to do something like this:

I have a string divided into an array. Example: "setVal strength 3"

lineArray[0] = setVal

lineArray[1] = strength

lineArray[2] = 3

I want to take lineArray[1] and add "Feats." to the beginning of it, so it it, for example, something like "Feats.strength" (which I can do with a string variable)

I then want to set that variable (Feats.strength, it's a double called strength in the Feats class) to lineArray[2] (which is a double).

else if(lineArray[0].equals("setVal") && lineArray.length == 2){

    //Take lineArray[1], which is the name of a variable in 
    another class, specifically Feats.strength, Feats.agility, etc.
    //Set that value in lineArray[1] to lineArray[2]

    //Something like
    set("Feats." + lineArray[1], lineArray[2]);

    Feats.resetStat();

}

Does that make any sense? Thanks for the help in advance!

You'll need to use reflection. Probably better to keep the properties in a map instead. But you know that already. — shmosel, Aug 18 '17 at 23:42
@Shomsel how would I go about that? I've tried literally everything I can think of. Do you have pointers? — Jacob B., Aug 18 '17 at 23:45
I just gave you pointers. If you've tried something, show what you've tried and explain where you're stuck. — shmosel, Aug 18 '17 at 23:46
Well, I stored the name in a map, but I don't know how to take the stored name and set that variable to lineArray[2] — Jacob B., Aug 18 '17 at 23:48
Wait... So that sets a variable by the name of lineArray[1] to the other one? I thought that set a map value to the second one — Jacob B., Aug 18 '17 at 23:50
Okaaayyy... So what I asked from the beginning then, how do I do that? — Jacob B., Aug 18 '17 at 23:53
How do you set a field using reflection? Check the internet, you should find an example or two or a million. — shmosel, Aug 18 '17 at 23:54
Possible duplicate of [Get variable by name from a String](https://stackoverflow.com/questions/13298823/get-variable-by-name-from-a-string) — , Aug 18 '17 at 23:54
Oh so you set a field through reflection? Thanks, that is all I was wondering — Jacob B., Aug 18 '17 at 23:55
**Don't use reflection** unless you know what you're doing. It can break everything, including compile-time safety, security and permormance. — MC Emperor, Aug 19 '17 at 00:26
@MCEmperor what would you recommend then? im trying to use reflection and i'm absolutelly lost (ive never used it before) what would you say i do? — Jacob B., Aug 19 '17 at 00:33
@JacobB. You could use a map: `map.put(lineArray[1], Long.parseLong(lineArray[2]))`. — MC Emperor, Aug 19 '17 at 10:05

wheeleruniverse · Answer 1 · 2017-08-19T00:36:47.370

Maybe something like this would work?

// Application.java
public class Application {

    public static void main(String[] args){
        String field = "setVal strength 3";
        Feats.resolveValue(field);

        String field2 = "getVal strength";
        Integer value = Feats.resolveValue(field2);

        String field3 = "clearAll";
        Feats.resolveValue(field3);
    }
}

--

// Feats.java
public class Feats {

    private static final Logger LOGGER = LoggerFactory.getLogger(Feats.class);
    private static final Map<String, Integer> ATTRIBUTES = new HashMap<>();

    public static String resolveString(String fieldInput){

         String response = null;
         String[] values = fieldInput.split(" ");
         Action action; 

         try {
             action = Action.valueOf(values[0].trim().toUppercase());

         } catch(Exception e){
             LOGGER.error("Not a valid Action in input: " + fieldInput);
             return response;
         }
         switch(action){
             case SETVALUE:
                setValue(values[1].trim(), values[2].trim());
                break;

             case CLEARALL:
                clearAll();
                break;

             case GETVALUE:
                response = getValue(values[1].trim());
                break;

             default:
                assert true;
         }

         return response;
    }

    private static void setValue(String attrName, String attrValue){
        ATTRIBUTES.put(attrName, attrValue);
    }

    private static String getValue(String attrName){
         return ATTRIBUTES.get(attrName);
    }

    private static void clearAll(){
        ATTRIBUTES.clear();
    }
}

--

// Action.java
public enum Action {
    SETVALUE, CLEARALL, GETVALUE
}

score 0 · Accepted Answer · answered Aug 19 '17 at 01:20

So I solved it. Thanks to @shmosel for telling me to use a field.

long temp = Long.parseLong(lineArray[2]);

try {
Feats.class.getField(lineArray[1]).set(lineArray[1], temp);;
} catch (NoSuchFieldException | SecurityException | IllegalArgumentException | IllegalAccessException e1) {
e1.printStackTrace();
}

Setting Variable Name from String in Java from User Input

2 Answers2