How to check if a string is empty or blank

Short answer

isEmpty() checks that a string has no characters, isBlank() checks that it contains nothing but whitespace:

void main() {
    IO.println("".isEmpty());
    IO.println("   ".isEmpty());
    IO.println("   ".isBlank());
}

Output:

true
false
true

The string may be null

You cannot call a method on null, so check the reference first:

boolean isBlank(String text) {
    return text == null || text.isBlank();
}
 
void main() {
    IO.println(isBlank(null));
    IO.println(isBlank(" \t "));
    IO.println(isBlank("Anna"));
}

Output:

true
true
false

A default value

Often an empty string should be replaced with a fallback value:

void main() {
    String name = "  ";
    String shown = name.isBlank() ? "Guest" : name.strip();
 
    IO.println("Hello, " + shown);
}

Output:

Hello, Guest

Removing empty strings from a list

Filter strings with isBlank() in a stream:

void main() {
    var lines = List.of("first", "", "  ", "second");
    var filled = lines.stream().filter(line -> !line.isBlank()).toList();
 
    IO.println(filled);
}

Output:

[first, second]

Common mistake

Checking text.length() == 0 or text.isEmpty() on null throws an exception:

void main() {
    String text = null;
    IO.println(text.isEmpty());
}

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.isEmpty()" because "<local1>" is null

Put text == null as the first condition — the || operator will not evaluate the second part.

Thanks for reading!

Short answer

The string may be null

A default value

Removing empty strings from a list

Common mistake

Functions used in this recipe

Thanks for reading!