how to check if a char is in a string java code example

Example 1: how to check if a char is a letter java

Character.isDigit(string.charAt(index)) //(JavaDoc) will return true if it's a digit
Character.isLetter(string.charAt(index)) //(JavaDoc) will return true if it's a letter

Example 2: java string contains char

/*
    This method returns true if the given string contains
    the char n. It is necessary due to the
    obsolescence of some compilers, which requires us
    to write our own contains method.
    */
    public static boolean contains_char (String main, char secondary)
    {
        boolean contains_result = false;
        for (int i = 0 ; i < input.length () ; i++)
        {
            if (input.charAt (i) == secondary)
            {
                contains_result = true;
                break;
            }
        }
        return contains_result;
    }

/*
for two chars:
*/
public static boolean contains_dualchar (String main, String secondary)
    {
        boolean contains_result = false;
        for (int i = 0 ; i < input.length () ; i++)
        {
            if (input.charAt (i) == secondary.charAt (0))
            {
                if (input.charAt (i + 1) == secondary.charAt (1))
                {
                    contains_result = true;
                    break;
                }
            }
        }
        return contains_result;
    }