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Not primitives, but, how about data structures like Set, List, ArrayList, HashMap? Any book to read that talks about all this? I have not clear many things.

Because once I declare a variable type Class I cannot assign values type Set, List, ArrayList to it, it throws me a mismatch type error.



It means I have to open the class with the IDE (Eclipse...

Many thanks for your answer. No, the code works, returns null as it is expected. But, it has to return null because the variables cannot store anything due to I can't assign them any additional type...

I'm a beginner, so, please be patient :D

I'm trying to make messages between classes coherent.
Hence, if I'm instancing a class I want to be able to declare the variable storing the instance by...

Many thanks for your help. I could fix it up thanks to you

I just started today with Java. The thing is as follows:

From class Notes in my class I have this properties and methods



import java.util.*;

public class Notes {