Assertions should be used to check something that should never happen, while an exception should be used to check something that might happen. For example, a function might divide by 0, so an exception should be used, but an assertion could be used to check that the harddrive suddenly disappears.

Should we use assert in Java?

Assertions are used to codify the requirements that render a program correct or not by testing conditions (Boolean expressions) for true values, and notifying the developer when such conditions are false. Using assertions can greatly increase your confidence in the correctness of your code.

Is it good practice to use assert?

Yes it is a very good practice to assert your assumptions. Read Design By Contract. assert can be used to verify pre conditions, invariants and post conditions during integration and testing phases. This helps to catch the errors while in development and testing phases.