How to convert a Java String to an Int

Java String/int FAQ: How do I convert a Java String to an int?

Solution

The most direct solution to convert a Java string to an integer is to use the parseInt method of the Integer class:

int i = Integer.parseInt(myString);

parseInt converts the String to an int, and throws a NumberFormatException if the string can’t be converted to an int type. For more information, see the following two examples. Therefore, a well-written function needs to account for this possible exception.

Example 1: A basic Java “String to int” conversion example

Ignoring the exception it can throw, all you need to convert a String to int is this one line of code:

int i = Integer.parseInt(myString);

If the String represented by the variable myString is a valid integer like “1”, “200”, and so on, it will be converted to a Java int. If it fails for any reason, the conversion will throw a NumberFormatException, so your code should be a little bit longer to account for this, as shown in the next example.

Example 2: A complete “String to int” example

Here’s the source code for a complete example program that demonstrates the Java String to int conversion process, handling for a possible NumberFormatException:

public class JavaStringToIntExample
{
  public static void main (String[] args)
  {
    // String s = "fred";  // use this if you want to test the exception below
    String s = "100";

    try
    {
      // the String to int conversion happens here
      int i = Integer.parseInt(s.trim());

      // print out the value after the conversion
      System.out.println("int i = " + i);
    }
    catch (NumberFormatException nfe)
    {
      System.out.println("NumberFormatException: " + nfe.getMessage());
    }
  }
}

Discussion

As you can see from this example, the Integer.parseInt(s.trim()) method is used to convert from the string s to the integer i in this line of code:

int i = Integer.parseInt(s.trim());

If the conversion attempt fails -- for instance, if you try to convert the Java String fred to an int -- the Integer parseInt method will throw a NumberFormatException, which you should handle in a try/catch block.

In this example, I don’t really need to use the String class trim() method, but in a real-world program you should use it, so that's why I’ve shown it here.

Related notes

While I’m in this neighborhood, here are a few related notes about the String and Integer classes:

• Integer.toString(int i) is used to convert in the other direction, from an int to a Java String.
• If you're interested in converting a String to an Integer object, use the valueOf() method of the Integer class instead of the parseInt() method.
• If you want to convert strings to other Java primitive fields, for example, a long, use methods like Long.parseLong(), and so on.

Summary

I hope this Java String to int example has been helpful. If you have any questions or comments, just leave a note in the Comments section below.