How to Check If a String is an Integer in Java

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  • 0:02 Java Strings
  • 1:25 Try/Catch
  • 4:19 Lesson Summary
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Lesson Transcript
Instructor: Martin Gibbs

Martin has 16 years experience in Human Resources Information Systems and has a PhD in Information Technology Management. He is an adjunct professor of computer science and computer programming.

Strings in Java are powerful because they can hold text, numbers, or any other characters. Sometimes, we need to know if the string is a number. This lesson will show you how to do this correctly.

Java Strings

Java Strings are great when you want to work with a wide variety of data in a single data type. They can hold text, integers, decimals, and doubles. But what if you want to check a given string to see if it is an integer, or if a string array contains an integer?

There are a few methods to accomplish this. We'll start with the parseInt function, which takes a string and tries to change it to an integer. Let's take a look at a basic example. For example, the following code creates a string that is a number, then uses parseInt to display the value.

String tester = new String("871");

The output would be 871. Remember, any integer is a whole number that can be positive, negative, or zero. Virtually any integer will pass the test. However, numbers beyond the range (such as 8589934592) won't pass. A decimal or fraction will also fail the test.

What if the string was not an integer? Technically, we could use parseInt to check and see if a string is an integer. But if the value was not an integer, Java would throw a very nasty error message. Let's say the string was Jane Eyre, and we tried the previous code. An error like this would display:

Java Exception Error


Whenever we're dealing with different data types, we need to make sure we have some code that can catch the exceptions. To do this we use the try and catch blocks around our test.

Thus, the next example is a little more complex. In our main section, we will set up a string as an array of strings, with some strings and some integers. We also have a second function called checkMe, which performs the actual check. We will again use parseInt, but with a little different twist.

First, let's take a look at the code that checks if the string has any integers. The function checkMe accepts one parameter (a string), then uses the parseInt function and returns TRUE if the value really is an integer. If parseInt fails, it will throw an exception. We catch any exceptions in the catch block and do nothing. We could show an error there, but it's not necessary. The last piece of code passes back the check. Is it valid or not? Is it an integer or not?

public static boolean checkMe(String s) {
  boolean amIValid = false;
  try {
   // s is a valid integer!
   amIValid = true;
  } catch (NumberFormatException e) {
   //sorry, not an integer
   // we just move on, but you could have code here
  return invalid;

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