Online

Java Platform Standard Edition 8 Documentation
http://docs.oracle.com/javase/8/docs/

Apache Ant Manual
http://ant.apache.org/manual/

JUnit
http://www.junit.org

Unit Testing in BlueJ
http://www.bluej.org/tutorial/testing-tutorial.pdf

Mockito
https://code.google.com/p/mockito/

Practical Unit Testing with JUnit and Mockito
Source code for examples
Source code for exercises

FindBugs
http://findbugs.sourceforge.net

PMD
http://pmd.sourceforge.net

Checkstyle
http://checkstyle.sourceforge.net

Artistic Style
http://astyle.sourceforge.net

 

Books

97 Things Every Programmer Should Know:
Collective Wisdom from the Experts
edited by Kevlin Henney

Debug It!
Find, Repair, and Prevent Bugs in Your Code
by Paul Butcher

Practical Unit Testing with JUnit and Mockito
by Tomek Kaczanowski

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Java 8 Lambdas: Pragmatic Functional Programming
by Richard Warburton

JUnit in Action, Second Edition
by Petar Tahchiev, et al.

Java SE 8 for the Really Impatient
by Cay S. Horstmann

Java The Complete Reference, 9th Edition
by Herbert Schildt