how Hashmap internally works and how to fix race condition and what is rehashing

L-1: Top10Employees list using Java 8 streams. Salary > 50000/- using Java 8 streams Salary > 50000/- and age < 40 (DOB) using Java 8 streams {1,2,3,4,5} sum = 6 Output {1,5} {2,4} using loops Questions: Java8 streams Functional interfaces HashMap internally working Red black tree @SpringBoot Application What happens without giving to the query params in @put method Schedulers CB pattern Uses of Kafka L-2: Spring boot & Microservices architect How to communicate Micro services How to call external APIs

Most Java related questions, architecture styles, design patterns, how to solve some specific problems, data bases with ORM and Hibernate, Spring boot related topics in much detail, microservices and orhcestrations, Kafka, AWS, Azure cloud and all about cloud infrastructure