using + and ? inside a string

using + and ? inside a string

Hi,

I'm having a problem with using special characters inside a string. I want to use the code:
var select_string = color_value + "+AND+" + size_value; where color_value and size_value are variables.

and I wish my results to be an url looking like this:
advanced_search_result.php?keywords=Metall+AND+17

However it looks like this:
advanced_search_result.php?keywords=Metall+AND+17

The + sign turns into +.

Any idea? I've tried the usual &....; and searched for java special text characters with no reslut.

Thanks!!
/Richard