How to Check if a String Is Not Null or Empty

Determining if a string is both not null and not empty is a common requirement in programming. Here's how to address this in Java:

The original code fragment checks for nullity and separately compares the string to an empty string using !=. However, this is not sufficient to handle cases where the string is null, as comparing a null reference to an empty string will cause a NullPointerException.

The correct approach is to use the isEmpty() method, which determines if the string has no characters. Here's the corrected code:

if(str != null && !str.isEmpty())

Using && (logical AND) ensures that both conditions must be met. The condition checking for nullity is evaluated first, and if str is null, the expression short-circuits, preventing the isEmpty() method from being called on a null reference.

Other options for checking if a string is empty include:

• str.length() == 0: This checks the length of the string, but does not account for whitespace.
• str.trim().isEmpty(): This checks the length of the trimmed string, which ignores leading and trailing whitespace. Since Java 11, this can be simplified to str.isBlank().

In summary, the isEmpty() method provides a concise and safe way to determine if a string is empty in Java.