how to check if a character is present in a string code example

Example 1: 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;
    }

Example 2: how to check if a string contains a character

public static boolean containsIgnoreCase(String str, char c) {
        str = str.toLowerCase();

        for (int i = 0; i < str.length(); i++) {
            if (str.charAt(i) == Character.toLowerCase(c)) {
                return true;
            }
        }
        
        return false;
    }