Double checked locking Article

Question

I was reading this article about \"Double-Checked locking\" and out of the main topic of the article I was wondering why at some point of the article the author uses the nex

Answer 1

Since Java 5, you can make double-checked locking work by declaring the field volatile.

See http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html for a full explanation.