Identifiers are case sensitive or not?

class Identifier3
{
public static void main(String alt[])
{
int number=10;
int Number=20;
int NUMBER=30;
System.out.println(number);
System.out.println(Number);
System.out.println(NUMBER);
}
}
/*
O/P:- 10 20 30
Explanation :- Java Identifiers are case sensitive.
*/