• Wikipedia: Java
• Java Documentation
• The Java Tutorials
• List of JVM languages

Books

• Core Java
• Thinking in Java / On Java 8 (books by Bruce Eckel)
• Effective Java, 3rd Edition
• Java Concurrency in Practice
• Java 8 Pocket Guide

IDEs

• Eclipse
• IntelliJ IDEA
• NetBeans

Java8 Stream API + Lambdas

• Get a Taste of Lambdas and Get Addicted to Streams by Venkat Subramaniam
• JDK 8 MOOC: Lambdas and Streams by Oracle
• YouTube playlist if the course is not available
• Oracle’s Lambda Quick Start