29.3. JavaScript Engine in Java

• Rhino: Originally the default JavaScript engine (developed by Mozilla) until Java 7. • Nashorn: Introduced in Java 8 to replace Rhino. It provides improved performance and better integration with Java. 📝 Note: Nashorn has been deprecated in Java 11 and removed in Java 15, but it remains an important historical and educational tool.

This chunk introduces two significant JavaScript engines used in Java - Rhino and Nashorn. Rhino was the initial engine established for Java, created by Mozilla, and served as the primary engine until Java 7. However, with enhancements in performance and integration capabilities, Nashorn was introduced in Java 8 to replace Rhino. Although Nashorn has been deprecated starting from Java 11 and completely removed in Java 15, it is still valuable for educational purposes.

Consider Rhino as an old reliable car that was used for years but became outdated as new technology emerged. Nashorn is like a newer model with better efficiency and features. Just as the old car taught drivers how to navigate the roads, Nashorn has trained developers on JavaScript integration in Java.

import javax.script.*; public class ScriptExample { public static void main(String[] args) throws ScriptException { ScriptEngineManager manager = new ScriptEngineManager(); ScriptEngine engine = manager.getEngineByName("nashorn"); engine.eval("print('Hello from JavaScript!');"); } }

This chunk provides a simple code example using Nashorn to execute JavaScript written within a Java program. It starts by importing the necessary scripting libraries and then defines a class ScriptExample. Inside the main method, a ScriptEngineManager is created to manage the scripting engine. The engine is fetched by its name 'nashorn', and finally, a JavaScript command is executed using the eval method, which prints a message to the console.

Think of this chunk as a chef (the Java program) who uses a special tool (the Nashorn engine) to cook a new dish (JavaScript code). The eval function is like the stove where the ingredients (commands) are heated up to create something tasty (output displayed on screen). Just as a recipe can change based on input, the engine lets Java adapt by executing different JavaScript commands.

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