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⚡ Let’s dive into the concept of channels in Java NIO — they’re at the heart of NIO’s power and flexibility.

✅ Core Features of Java NIO (New I/O)

🔹 1. Channels

• Abstraction for reading/writing data to files, sockets, etc.
• Can be bi-directional (read + write)
• Work with Buffers, not streams

FileChannel channel = new FileInputStream("file.txt").getChannel();

🧠 Summary

✅ What is a Channel?

In Java NIO, a Channel is like a modern alternative to InputStream/OutputStream, but more powerful.

It represents a connection to a data source (like a file, socket, etc.), through which you can read, write, or both.

⚙️ Let’s break down the difference between IO (java.io) and NIO (java.nio) — two major APIs for handling input/output in Java.

🔐 In Java 8, creating a Base64 encoder and decoder is super simple using the built-in java.util.Base64 class.

Let’s walk through how to create and use both.

🧩 In Java 8, the class introduced for encoding and decoding data, especially in Base64, is:

✅ java.util.Base64

This class provides built-in support for Base64 encoding and decoding — no more need for third-party libraries or Apache Commons!

⚙️ GraalVM is one of the most exciting technologies in the Java ecosystem today. Let’s break it down simply and clearly.

✅ What is jjs?

jjs was a command-line tool introduced in Java 8 that allowed you to run JavaScript code directly using the Nashorn JavaScript engine.

Think of it as a mini JavaScript REPL or script runner inside your JDK.

🔹 Example Usage

jjs

You’d get an interactive shell like this:

jjs> print("Hello from Nashorn!");
Hello from Nashorn!

Or run a script file:

jjs myscript.js

✅ What Could You Do with jjs?

• Run JavaScript code from the terminal
• Import and use Java classes from JavaScript
• Do quick scripting or automation tasks using the JVM

🔧 Example: Calling Java from JavaScript

// hello.js
var ArrayList = Java.type("java.util.ArrayList");
var list = new ArrayList();
list.add("Java + JS");
print(list.get(0));

Then run:

jjs hello.js

❌ Deprecation & Removal

Why? Because Nashorn couldn’t keep up with newer JavaScript standards (ES6+), and newer tools like GraalVM replaced it.

🧠 Summary

🧠 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.

✅ What Is a Repeatable Annotation?

It means you can write something like this:

@Hint("first hint")
@Hint("second hint")
public class MyClass { }

To make this possible, you need to define:

1. The repeatable annotation
2. A container annotation that holds multiple instances