How can I check if a single character appears in a string?

Question

In Java is there a way to check the condition:

"Does this single character appear at all in string x"

without using a loop?

Thank you,

Answer 1

String.indexOf()

Answer 2

• String.contains() which checks if the string contains a specified sequence of char values
• String.indexOf() which returns the index within the string of the first occurence of the specified character or substring (there are 4 variations of this method)

Answer 3

To check if something does not exist in a string, you at least need to look at each character in a string. So even if you don't explicitly use a loop, it'll have the same efficiency. That being said, you can try using str.contains(""+char).

Answer 4

Yes, using the indexOf() method on the string class. See the API documentation for this method

Answer 5

I'm not sure what the original poster is asking exactly. Since indexOf(...) and contains(...) both probably use loops internally, perhaps he's looking to see if this is possible at all without a loop? I can think of two ways off hand, one would of course be recurrsion:

public boolean containsChar(String s, char search) {
    if (s.length() == 0)
        return false;
    else
        return s.charAt(0) == search || containsChar(s.substring(1), search);
}

The other is far less elegant, but completeness...:

/**
 * Works for strings of up to 5 characters
 */
public boolean containsChar(String s, char search) {
    if (s.length() > 5) throw IllegalArgumentException();

    try {
        if (s.charAt(0) == search) return true;
        if (s.charAt(1) == search) return true;
        if (s.charAt(2) == search) return true;
        if (s.charAt(3) == search) return true;
        if (s.charAt(4) == search) return true;
    } catch (IndexOutOfBoundsException e) {
        // this should never happen...
        return false;
    }
    return false;
}

The number of lines grow as you need to support longer and longer strings of course. But there are no loops/recurrsions at all. You can even remove the length check if you're concerned that that length() uses a loop.