Question

If I import and use a single class from another package, will it include all files from the package?

for example, if I use only a single class from the mylibrary package which is called MyFunctions, will the following include all classes or not?

import my.example.mylibrary.*;

compared with:

import my.example.mylibrary.MyFunctions;

Answer 1

No

The import does not include anything into your program.

Classes are loaded when they are used, and not before. So the only thing the import is to help you to avoid typing the whole class name.

For instance it is much better to type ( and to read ) :

import my.example.mylibrary.SomeClass;
import java.util.List;
import java.util.ArrayList;
...
SomeClass some = new SomeClass();
List<SomeClass> list = new ArrayList<SomeClass>();
list.add( some );
etc.. 

than

// no import 
... 
my.example.mylibrary.SomeClass some = new my.example.mylibrary.SomeClass();
java.util.List<my.example.mylibrary.SomeClass> list = new java.util.ArrayList<my.example.mylibrary.SomeClass>();
list.add( some );

And yet, they perform exactly the same.

Also, bear in mind that using

import some.packagename.*;

vs.

import some.packagename.Each;
import some.packagename.Single;
import some.packagename.Class;
import some.packagename.ByLine;

Have exactly the same performace, except the firs it faster ( and dirtier ) and the second is clearer.

Always!! use the second form in production and/or when someone else needs to see your code.