Several GitHub repositories host digital copies, summaries, and implementation samples for (commonly known as the ). PDF and E-Book Resources on GitHub
The "red book" contains hundreds of code snippets in Java (and some Scala). Typing these out manually is tedious and error-prone. This is why GitHub is the most critical resource in your search.
While many users search for "free PDFs," high-quality technical documentation is best sourced officially to ensure you are looking at the latest errata and high-resolution diagrams.