Rhino: Java numbers don't behave like Javascript numbers -

i have instance of java class accessible in javascript program

public class contentprovider {   public object c(int n) {     switch (n) {       case 1: return 1.1;       case 2: return 2.2;       case 3: return 3.3;       case 4: return "4";       case 5: return new java.util.date();     }     return null;   } } 

this code inside main():

scriptenginemanager mgr = new scriptenginemanager(); scriptengine engine = mgr.getenginebyname("javascript"); engine.put("ctx", new contentprovider());  res = engine.eval("ctx.c(1)");  system.out.printf("rhino:> %s (%s)%n"         , res         , res != null ? res.getclass().getname() : null ); 

the simple expression ctx.c(1) prints:

rhino:> 1.1 (java.lang.double) 

now here happens ctx.c(1) + ctx.c(2):

rhino:> 1.12.2 (java.lang.string) 

and (ctx.c(1) + ctx.c(2)) * ctx.c(3):

rhino:> nan (java.lang.double) 

rhino performing string concatenation instead of number arithmetics! following program works expected instead:

engine.put("a", 1.1); engine.put("b", 2.2); engine.put("c", 3.3); res = engine.eval("(a + b) * c"); 

outputs:

rhino:> 10,89 (java.lang.double) 

this strange feature of rhino: java number set engine.put("one", new double(1)) works expected, while result of java method depends on return type declared method itself, read reflection api:

• if it's primitive, double, it's converted javascript number
• otherwise it's handled other host objects , + means concatenation, either object in sample double

you can configure behavior wrapfactory.setjavaprimitivewrap(false) on wrapfactory in current context. way rhino code can kept in bootstrap lines of program , doesn't clutter contentprovider (which guess sort of configuration proxy)

from live javadoc of wrapfactory.isjavaprimitivewrap()

by default method returns true indicate instances of string, number, boolean , character should wrapped other java object , scripts can access java method available in these objects

so can set flag false indicate java number's should converted javascript numbers. takes 2 lines of code

context ctx = context.enter(); ctx.getwrapfactory().setjavaprimitivewrap(false); 

here the gist full code used test