Libraries

I’m quite new to OOP and I’m struggling to understand a concept about libraries.
I thought libraries are “pre written classes” that I can access, just like any other class.

I’ve used
java.util.Random;
java.util.Scanner;
java.io.FileWriter;
before.

Before I can access a method of these libraries I first have to initialize an object.
f.e.
Random random = new Random();
Scanner scanner = new Scanner(System.in);
FileWriter fileWriter = new FileWriter(“example.csv”);

Now I’m starting to work with arrays.
After importing the array library I can instantly access the method Array.toString()
Why do I not have to initialize an object of the class (Arrays arrays = new array;) like I usually have to?

Thanks for your help, I appreciate it.