Write a Java program that checks whether the given string contains only digits $($ASCII characters $0-9)$ and returns true or false.

You must include a simple constructor and perform your core counting logic in a class method named OnlyDigits $($not in main$).$

Test your program with the given strings:

$"95784846896"$

$"3018604000"$

$"9$A$48$@$9$Z$96"$

Hint: You may use the Java Character.isDigit$()$ or String.matches$()$ methods.