How can we Working with Compilable Scripts

import javax.script.Compilable;
import javax.script.CompiledScript;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class JDK6TabSample {
public static void main(String args[]) {
ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("javascript");
engine.put("counter", 0);
if (engine instanceof Compilable) {
Compilable compEngine = (Compilable) engine;
try {
CompiledScript script = compEngine.compile("function count(){counter=counter+1;return counter;}; count();");
System.out.println(script.eval());
System.out.println(script.eval());
System.out.println(script.eval());
} catch (ScriptException e) {
System.err.println(e);
}
} else {
System.err.println("Engine can't compile code");
}
}
}
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