Sites:

Stackoverflow

The most popular website in the programming world with millions of good questions and answers

Segmentfault

中国版的stackoverflow

Github

Where software is built

Coursera

The best site for video lectures.

Tutorialspoint

The largest Tutorials Library on the web

ideone

Online Compiler and IDE >> C/C++, Java, PHP, Python, Perl and 40+ other compilers and interpreters

DZone

https://dzone.com/

Java SE Technical Documentation

http://docs.oracle.com/javase/8/

Java World

http://www.javaworld.com/

IBM developerWorks

http://www.ibm.com/developerworks/java/

Program Creek:one of the top 100 Java blogs

http://www.programcreek.com/

javased :Code examples for popular API classes

http://www.javased.com/

LeetCode

https://leetcode.com/

The top 100 Java blogs

100 High-Quality Java Developers’ Blogs

winterbe Blog

http://winterbe.com/

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Books:

Thinking in Java (4th Edition)

Effective Java (2nd Edition)

Head First Java (2nd Edition)

 

Top 10 Books For Advanced Level Java Developers

 Javalobby Readers’ Choice: Top Java Books 

Knowledge:

Java Language and Virtual Machine Specifications

 JVM:

JVM运行时是什么样子？

JVM 的 工作原理，层次结构 以及 GC工作原理

深入理解JVM
https://segmentfault.com/a/1190000004206269

JVM Internals
http://blog.jamesdbloom.com/JVMInternals.html

*Top 8 Diagrams for Understanding Java

 

Java Code To Byte Code
http://blog.jamesdbloom.com/JavaCodeToByteCode_PartOne.html

 

refer:
http://www.programcreek.com/2013/09/top-10-websites-for-advanced-level-java-developers/