Java.Java8.What is Nashorn?

🧠 What is Nashorn?

Nashorn is a JavaScript engine built into the Java 8 platform.

It allows you to run JavaScript code inside a Java application.

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🔹 Key Points:

Feature	Description
Language	JavaScript (ECMAScript 5.1 standard)
Introduced In	Java 8 (jdk.nashorn.api.scripting)
Based On	The JSR 223 scripting API
Performance	Faster than the old Rhino engine
Interoperability	Allows calling Java classes and methods from JavaScript
Deprecated	Since Java 11, and removed in Java 15 (in favor of GraalVM etc.)

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✅ Basic Example: Run JavaScript from Java

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

public class NashornExample {
    public static void main(String[] args) throws Exception {
        ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
        engine.eval("print('Hello from JavaScript!');");
    }
}

🔹 Output:

Hello from JavaScript!

✅ Call Java from JavaScript

engine.eval("var list = new java.util.ArrayList(); list.add('hello'); print(list.get(0));");

🔥 Use Cases (Back in the Day)

• Embedding scripting support in Java apps
• Dynamic configuration or plugins
• Executing user-defined scripts safely (sandboxed)

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❌ Why It’s Deprecated

• JavaScript evolved quickly (ES6, ES7, etc.)
• Nashorn couldn’t keep up
• Replaced by modern solutions like GraalVM, which support modern JS

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✅ Alternatives Now

Use Case	Alternative
JavaScript scripting	GraalVM JavaScript
General scripting	JSR-223 engines (e.g., Groovy, Kotlin, etc.)
Polyglot applications	GraalVM (multi-language support)