1. basic java knowledge, such as inheritance, polymorphism , dynamic binding, static binding, abstract class, interface, inner class, nested class 2. Data structure array, list, 3. Algorithm: binary search, sort 4. Java programming on site 5. design pattern: singleton, factory

Contacted me through email.First Finish the Coding challenge on Hackerrank .Then tell him the compensation expectation.I finished the challenge ,I think I definitely passed the coding challenge. But after two hours challenge the recruiter told me we don't have same salary expectations so we can't move forward. How bad this experience would be? you waste two hours and they told you a result that you might know way much earlier.