JavaからJavaScript(Rhino)呼び出し JavaObjectのKey

gistfile1.java

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

public class ScriptingForJavaScript {
    public static void main(String[] args) throws Exception {
        ScriptEngineManager factory = new ScriptEngineManager();
        ScriptEngine engine = factory.getEngineByName("js");
    
        Object obj= new Object();
        engine.put("obj", obj);

        try {
            engine.eval("println(obj);");
            engine.eval("for (var i in obj) { println(i); }");
        } catch (ScriptException ex) {
            ex.printStackTrace();
        }
    }
}