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This exercise is already available in your IntelliJ as a project. What you need to do is described in the comments at the top of the file in src/main/java/.

package basics;

public class StringUtils {


    /**
     * Split a string according to a delimiter
     *
     * @param str The string to split
     * @param delimiter The delimiter
     * @return An array containing the substring which fall
     *          between two consecutive occurence of the delimiter.
     *          If there is no occurence of the delimiter, it should
     *          return an array of size 1 with the string at element 0
     */
    public static String [] split(String str, char delimiter){
         return null;
    }


    /**
     * Find the first occurence of a substring in a string
     *
     * @param str The string to look in
     * @param sub The string to look for
     * @return The index of the start of the first appearance of
     *          the substring in str or -1 if sub does not appear
     *          in str
     */
    public static int indexOf(String str, String sub){
         return 0;
    }


    /**
     * Convert a string to lowercase
     *
     * @param str The string to convert
     * @return A new string, same as str but with every
     *          character put to lower case.
     */
    public static String toLowerCase(String str){
         return null;
    }


    /**
     * Check if a string is a palyndrome
     *
     * A palyndrome is a sequence of character that is the
     * same when read from left to right and from right to
     * left.
     *
     * @param str The string to check
     * @return true if str is a palyndrome, false otherwise
     */
    public static boolean palindrome(String str){
         return false;
    }


}