String.indexOf's arguments should not be reversed JAVA-E1089

When searching for a character in a string using String.indexOf(), one should be careful to not mix up the order of its arguments.

One of the overloads of indexOf() takes two arguments; the first is the character to search for and the second is the index to start searching from. Both these parameters are integers, and this opens up new avenues for confusion due to type promotion rules.

Bad Practice

String s = "Hello, World!";

int index = s.indexOf(7, 'o'); // This is the wrong order!

In the example above, the arguments are passed in the wrong order. The first argument should be the character to search for, and the second should be the starting index to begin the search from. Here, however, the first argument is an integer, and the second argument is a character.

Due to type promotion, narrower types such as char will be converted automatically if a wider type (like int) was expected. In this case, the method will return the index of the character represented by the integer value 7, rather than the index of the 'o' character.

Recommended

Switch the arguments around.

int index = s.indexOf('o', 7);