What is the use of static class in java

Question

If you make a class static which is not inside another class it says static not allowed here.but you can use static with an inner class like

Answer 1

https://www.sololearn.com/learn/Java/2159/

https://www.sololearn.com/learn/CSharp/2666/

https://www.sololearn.com/learn/CSharp/2672/

https://www.sololearn.com/learn/JUMP_LINK__&&__Python__&&__JUMP_LINK/2473/