Explain garbage collection in java? Diff between JVM, JRE, JDK? comparable vs comparator how spring boot app starts? mapping in hibernate? sql joins

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Garbage collection in Java is a process of automatically reclaiming memory by destroying unused objects.

Garbage collection in Java is performed by the JVM to reclaim memory occupied by objects that are no longer in use.
JVM stands for Java Virtual Machine, JRE stands for Java Runtime Environment, and JDK stands for Java Development Kit.
Comparable interface is used to define the natural ordering of objects, while Comparator interface is used to define custom ordering logic.
Spring Boot application starts by creating an instance of SpringApplication and running the main method.
In Hibernate, mapping is the process of defining how Java objects are mapped to database tables.
SQL joins are used to combine rows from two or more tables based on a related column between them.

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