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Main Textbooks:
eBook 1: Think Java: How to Think Like a Computer Scientist
Online interactive html version
eBook 2: Introduction to Programming Using Java
Online html version
Other references:
The Java Language Specification, Java SE 11 Edition
The Java Virtual Machine Specification, Java SE 11 Edition
Java style guide: Google’s recommendation for open source java contributions, highly recommended as a guide for formatting program text and more
Oracle’s own tutorials on Java