Section 1.5. Assertions

1.5. Assertions

We clarify our code by liberal use of the assert statement. Each occurrence of assert is followed by a boolean expression that is expected to evaluate to true. If assertions are enabled and the expression evaluates to false, an AssertionError is thrown, including an indication of where the error occurred. Assertions are enabled by invoking the JVM with the -ea or -enableassertions flag.

We only write assertions that we expect to evaluate to TRue. Since assertions may not be enabled, an assertion should never have side effects upon which any nonassertion code depends. When checking for a condition that might not hold (such as confirming that the arguments to a method call are valid), we use a conditional and throw an exception explicitly.

To sum up, we have seen how generics, boxing and unboxing, foreach loops, and varargs work together to make Java code easier to write, having illustrated this through the use of the Collections Framework.