1. Write a static method

   public static boolean appearsIn(String s, char c)

   that, given a string s and a character c, verifies whether c appears in s.
   For example, the call appearsIn("pippo", 'i') should return true.

   Solution

2. Write a static method

   public static int occurrences(String s, char c)

   that, given a string s and a character c, returns the number of occurrences of c in s.
   For example, the call occurrences("pippo",'p') should return 3.

   Solution

3. Write a static method

   public static String underscore(String s)

   that, given a string s, returns a string obtained from s by replacing each blank with the underscore character ('_').
   For example the call underscore("pippo and topolino") should return the string "pippo_and_topolino".

   Solution

4. Write a static method

   public static String reverse(String s)

   that, given a string s, returns the string constituted by the characters of s in inverse order.
   For example the call reverse("pippo") should return the string "oppip".

   Solution

5. Write a static method

   public static String removeVocals(String s)

   that, given a string s, returns a string obtained from s by removing all vocals.
   For example the call removeVocals("pippo") should return the string "ppp".

   Solution

6. Write a static method

   public static boolean palindrome(String s)

   that, given a string s, returns the boolean value true if the string is a palindrome, false otherwise.
   A string is palindrome if, when the string spelled from left to right it is equal to the string spelled from right to left. (e.g., "anna" and "ailatiditalia" are palidrome strings).

   Solution

7. Write a static method

   public static void permutations(String s, PrintStream p)

   that, given a string s and a PrintStrem p, prints on p all strings obtained by permuting the characters of s.
   For example, the call permutations("abc", System.out) should print the following on standard output:

   abc
   acb
   bac
   bca
   cab
   cba
   

   Solution

Class Main to test the methods above.