How to convert a Java String to an Int

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

Answer: Convert a string to an integer with the parseInt method of the Java Integer class. The parseInt method is to convert the String to an int and throws a NumberFormatException if the string cannot be converted to an int type.

Examples

Java String to int conversion

Overlooking the exception it can throw, use this:

int i = Integer.parseInt(myString);

If the String signified by the variable myString is a valid integer like “1”, “200”, and it will be converted to a Java int. If it fails for any reason, the change can throw a NumberFormatException, so the code should be a little longer to account for this.

Complete String to int

Here is the source code for a whole instance program that demonstrates the Java String to int conversion method, control 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());
    }
  }
}

Let’s discuss

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

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

If the change attempt fails – in case, if you can try to convert the Java String fred to an int — the Integer parseInt process will throw a NumberFormatException, which you must handle in a try/catch block.

In this case, it’s not essential to use the String class trim() method but in a real-world program, you must use it, so that’s why I’ve shown it here.

Since we’re talking about this, here are a few related notes about the String and Integer classes:

• Integer.toString(int i) is used to convert in the further direction, from an int to a Java String.
• If you’re concerned with converting a String to an Integer object, use the valueOf() method of the Integer class instead of the parseInt() method.
• If you need to convert strings to additional Java primitive fields, use methods like Long.parseLong(), and so on.

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