How can I make a query using variable filter value?

I am trying to make a query using Jena ARQ as follows:

static public final String NL = System.getProperty("line.separator") ;

//some codes

    String prolog = "PREFIX rdf: <"+ RDF.getURI()+"> 
    PREFIX rdfs: <"+RDFS.getURI()+"> 
    PREFIX myproject:<http://www.myproject.com/ontologies/myproject.owl#>" ;

    String queryString = prolog + NL 
+ "SELECT ?individu WHERE {
      ?individu rdf:type myproject:Plant. 
      ?individu myproject:height ?height.  
      FILTER(?height <= 6.0). 
     ?individu myproject:diameter ?diameter. 
     FILTER(?diameter = 0.5)} 
    ORDER BY ?individu
}" ;

//some codes

Using this code my program works well. As we can see that I use constant filter values for height and diameter (6.0 and 0.5 respectively). However actually what I want is not a constant filter values. Instead I want variable filter values. This is similar to PreparedStatement in MySQL. I need this because the query must change dynamically based on user input. So, my question is: how can I make a query using variable filter value? Thanks.