Effective java Item 38: Check parameters for validity is the general principle of detecting errors as soon as possible. Also known as the Fail fast it is good practice to notify consumers up front which will help to determine and detect source of errors. This example will show common ways to check parameters for validitiy with guava's preconditions and apache commons Validate.
Something to be aware of is there a difference in the exceptions that these two approachs throw. For instance, check parameter is not null in Guava throws a NullPointerException vs Apache commons Validator throws IllegalArgumentException. My recommendation is pick one within your applications and stick with it.
Check parameter is not null
Check state of object
An example of where you may call a methods initialize method before any other method.