How to convert a Java String to an Int

By Alvin Alexander. Last updated: July 30, 2024

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.