Java's assertion errors act as an internal alarm system for developers, signaling when a fundamental assumption in the code's logic has been violated. Unlike exceptions that handle predictable runtime issues, assertion errors indicate a breakdown in the code's internal logic or design assumptions. Assertions in Java, which are disabled by default and must be enabled using the -ea flag, help developers test assumptions during development and testing phases by using statements like `assert condition : errorMessage`. These assertions are beneficial for catching logical errors and impossible conditions that should not occur in functioning code, while exceptions are more suited for handling expected failure scenarios or validating external inputs. Best practices suggest using clear, actionable messages in assertions and relying on exceptions for critical checks in production environments, as assertions are often disabled in such settings. Understanding and effectively utilizing assertion errors can streamline debugging and enhance code reliability, with tools like Rollbar offering additional support by capturing and analyzing runtime errors.