How do I convert a String to a long with Java?

Question: How do I convert a String to a long with Java?

Answer: The Long class includes a method named parseLong() that serves just this purpose. An example of a simple program that performs this conversion is shown below:

public class StringToLong {

   public static void main (String[] args) {

      // String s = "fred";    // do this if you want an exception

      String s = "100";

      try {
         long l = Long.parseLong(s.trim());
         System.out.println("long l = " + l);
      } catch (NumberFormatException nfe) {
         System.out.println("NumberFormatException: " + nfe.getMessage());
      }

   }
}

Other Java String to long notes

  • Long.toString(long l) is used to convert in the other direction, from long to String.
  • If you're interested in converting a String to a Long object, use the valueOf() method of the Long class instead of the parseLong() method.

trim()?

why do you use trim() here?
I have read explanation for that, but i do not get it.
please explain it to me
tanx

Long.parseLong throws an exception on spaces

The trim() method removes any whitespace from around the value you're given. So, if you get a String like " 11 ", it will turn that String into "11" before attempting the conversion.

This is needed because the Long.parseLong() method will throw an exception if you give it a String with spaces in it, like " 11 ".

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