Question

Which of the following correctly tests if str is the empty string? (Assume that all the usual methods are available.) A. str == ""

B. str == 0
C. str.length = 0
D. str.length() == 0

Answer 1

The correct way to test if a string named str is empty is by checking if its length is 0, as in str.length() == 0.

Step-by-step explanation:

To test if str is the empty string, the correct method is to compare the length of the string to 0. Therefore, the correct answer is D. str.length() == 0. This method calls the length() method on the string object str to return the number of characters. If there are no characters, the length is 0, which means the string is empty.

Option A is incorrect because although str == "" effectively checks if the string is empty, it's not a test of the string's length per se, but a direct comparison to an empty string literal. Option B, str == 0, is incorrect because it compares the string to the number 0, which is a type mismatch and would not accurately test for an empty string. Option C, str.length = 0, is actually a syntactical error, as it attempts to assign a value to a method call instead of comparing values.