What happens if the read/write stream is not closed?

Question

Java

Hello. The question, I'm sure, is simple, but nevertheless it puzzled me.
What happens if we don't close the read or write stream to a file or database? Well, records, for example, the .flush method (using Java as an example) may not be called (although we can call it, instead of the close method) for the writing classes and new data will not be entered into the file, but what could be fraught with a similar situation for the reader class?

Answer 1

File lock.
Increase in memory consumption.
Etc.