Udemy's appeal for OCP Java SE 21 prep is the price — self-paced video courses and practice-test sets from independent instructors, usually at a fraction of official training rates. Udemy hosts a range of 1Z0-830 practice-test courses with full timed tests and explanations, useful alongside a study guide.
The gap is the same one that shows up across any self-paced marketplace: a course or practice-test set can't tell you specifically which of Java SE 21's object-oriented concepts, streams and lambdas, collections, concurrency, and I/O topics you're actually weak in. You finish knowing you worked through everything, not knowing whether you've retained enough to pass.
Edureify's Diagnostic maps your understanding across Java SE 21's object-oriented concepts, streams and lambdas, collections, concurrency, and I/O topics on day one, and the Readiness Score keeps updating as you practice — so instead of a vague sense of completion, you get a specific, evolving answer.