Short-circuit AND Operator

You may have noticed something in answering the question: you can get the correct answer to the question by evaluating just the first part of the expression:

12 < 6 && 18 > 1
------ 
false

Since false && anything is false, there is no need to continue after the first false has been encountered. In fact, this is how Java operates:

To evaluate X && Y, first evaluate X. If X is false then stop: the whole expression is false. Otherwise, evaluate Y then AND the two values.

This idea is called short-circuit evaluation. Programmers frequently make use of this feature. For example, say that two methods that return true/false values are combined in a boolean expression:

if ( methodThatTakesHoursToRun() && methodThatWorksInstantly() )
   ....