Programming Languages & Frameworks

Hi,

I am pretty new to Java Script in javax.script package. I am just wondering and scratching my head off to understand the difference between
Compilable.compile(String script) and ScriptEngine.eval(String script).

Let’s assume I get somehow the “engine” object:

    ScriptEngineManager factory = new ScriptEngineManager();

    ScriptEngine engine = factory.getEngineByName("JavaScript");

Let’s say I have a script string like this: string = “function raiseAlarm()

{

    var now = new java.util.Date();

    print("major " + now);

}”

If I evaluate it and call it this way:

engine.eval(string);

Invocable inv = (Invocable) engine;

1. inv.invokeFunction("raiseAlarm”);

… Well it works (no compilation involved)

However if I compile it and then not evaluate it and then try to call a method (“raiseAlarm”) I get an exception java.lang.NoSuchMethodException: No such function raiseAlarm. (Something like this):

Compilable compEngine = (Compilable) engine;

script = compEngine.compile(string);

Invocable inv = (Invocable) engine;

1. inv.invokeFunction("raiseAlarm”);

So my question is what is the point of compiling that script string if I still have to evaluate it to get a result without an error? What have I achieved by compiling it?

Kind Regards,

Janusz