Validate input $-$ isInteger$()$

Java is a type$-$safe language. This means that it does not convert data from one type to another automatically.

The method isInteger$()$ must check the input to the console to discover if it is truly an integer. Return true if so and return false if it is not an integer.

In this case, we read the input in as a String, and need to confirm that each character is actually a digit.

Tip: It is helpful to think of a String as a List of characters because this is how Java creates it$.$ You can treat it as a List when checking the value of individual Characters in that String.