getScript().callFunction will always return an object. Initially you have to store it in an object and then parse it to Boolean as shown below:
Object val = getScript("ScriptName").callFunction("FunctionName", pass arguments for the function if any);
Parse as below
Boolean giveme = Boolean.parseBoolean(val.toString());
System.out.println("Return val: "+giveme);
This should solve your problem. Please let me know if it does not..