Assertion should not be used to replace exception handling. Exception handling deals with unusual circumstances during program execution. Assertions are to assure the correctness of the program. Exception handling addresses robustness and assertion addresses correctness. Like exception handling, assertions are not used for normal tests, but for internal consistency and validity checks. Assertions are checked at runtime and can be turned on or off at startup time.

Do not use assertions for argument checking in public methods. Valid arguments that may be passed to a public method are considered to be part of the method's contract. The contract must always be obeyed whether assertions are enabled or disabled.

Do not use assertions for argument checking in public methods. Valid arguments that may be passed to a public method are considered to be part of the method's contract. The contract must always be obeyed whether assertions are enabled or disabled.

Another good use of assertions is place assertions in a switch statement without a default case. For example,

switch (month) {
  case 1: ... ; break;
  case 2: ... ; break;
  ...
  case 12: ... ; break;
  default: assert false : "Invalid month: " + month
}