How to use Java Objects in JavaScript

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


public class JavaObjectDemo
{
public static void main(String[] args) throws Exception
{
ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine jsEngine;
jsEngine = manager.getEngineByExtension("js");
jsEngine.eval("importPackage(javax.swing);var optionPane =JOptionPane.showMessageDialog(null, 'Hello!);");
}
}