What's the best way to check if a String represents an integer in Java?

Question

I normally use the following idiom to check if a String can be converted to an integer.

public boolean isInteger( String input ) {
    try {
        Integer.         


        

Answer 1

I believe there's zero risk running into an exception, because as you can see below you always safely parse int to String and not the other way around.

So:

1. You check if every slot of character in your string matches at least one of the characters {"0","1","2","3","4","5","6","7","8","9"}.

   if(aString.substring(j, j+1).equals(String.valueOf(i)))
   

2. You sum all the times that you encountered in the slots the above characters.

   digits++;
   

3. And finally you check if the times that you encountered integers as characters equals with the length of the given string.

   if(digits == aString.length())
   

And in practice we have:

    String aString = "1234224245";
    int digits = 0;//count how many digits you encountered
    for(int j=0;j

And the results are:

It's an integer!!

It's not an integer!!

Similarly, you can validate if a String is a float or a double but in those cases you have to encounter only one . (dot) in the String and of course check if digits == (aString.length()-1)

Again, there's zero risk running into a parsing exception here, but if you plan on parsing a string that it is known that contains a number (let's say int data type) you must first check if it fits in the data type. Otherwise you must cast it.

I hope I helped