This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
.length is a fundamental property of any array. It's "defined" in the Java Language Specification. Since an array is an Object, you can also call methods such as equals(), hashCode(), getClass(), notify(), wait(), etc.