use java

21. As mentioned in the text, a Java identifier consists of one or more characters. The first character must be an uppercase or lowercase letter of the alphabet, an underscore _, or a dollar sign $. Each remaining character must be an uppercase or lowercase letter of the alphabet, a digit 0-9, an underscore, or a dollar sign. Write a Java program that reads in a line of characters and prints out whether the line of characters is a legal Java identifier