Java programming. Please do not use arrays to solve this problem. thanks

P5.4 Write a method public static String middle(String str) that returns a string containing the middle character in str if the length of str is odd, or the two middle characters if the length is even. For example, middle("middle") returns "dd". P5.5 Write a method public static String repeat(String str, int n) that returns the string str repeated n times. For example, repeat ("ho", 3) returns "hohoho". P5.6 Write a method public static int countVowels (String str) that returns a count of all vowels in the string str. Vowels are the letters a, e, i, o, and u, and their uppercase variants