Write the body for the methods described below.
Once you have completed each method, copy and paste the code in this file into your class. Then run the test() method and you will get feedback on your code.
Part I
int countF(String str)
Description: This method returns the number of times that the the lower case letter ‘f’ occurs in str .
| Method Call | return value/output |
| countF(“abcdef”) | 1 |
| countF(“abcdfef”) | 2 |
| countF(“fff”) | 3 |
| countF(“xxx”) | 0 |
boolean hasN_Fs(String str, int n )
Description: This method returns true if str has exactly n occurrences of the letter ‘f’ in it.
String threeTimes(String str)
Description: This method returns the String str concatenated with itself three times
| Method Call | return value/output |
| threeTimes(“foog”) | “foogfoogfoog” |
| threeTimes(“abc”) | “abcabcabc” |
| threeTimes(“zt”) | “ztztzt” |
| threeTimes(“”) | “” |
String nTimes(String str, int n)
Description: This method returns the String str concatenated with itself n times
| Method Call | return value/output |
| nTimes(“fg” , 2 ) | “fgfg” |
| nTimes(“abc” , 0 ) | “” |
| nTimes(“zt” , 3 ) | “ztztzt” |
| nTimes(“uiz” , 4 ) | “uizuizuizuiz” |
int countMiddleChar(String str)
Precondition: str.length() ≥ 3.
Description: This method returns the number of times the middle letter of str appears in str.
| Method Call | return value/output |
| countMiddleChar(“acbcb” ) | 2 |
| countMiddleChar(“acbcx” ) | 1 |
| countMiddleChar(“bbbbb” ) | 5 |
| countMiddleChar(“xytbtzy”) | 1 |
int indexOf(String haystack, String needle)
Description: Write your own indexOf() method. Obviously, you cannot make use of the String’s built in indexOf() method. This method returns the index of the first occurrence of needle in haystack . (Full credit if you can get this to work with Strings whose length is greater than 1).
| Method Call | return value/output |
| indexOf(“acxb”, “x” ) | 2 |
| indexOf(“zazt”, “z” ) | 0 |
| indexOf(“tayv”, “g” ) | -1 |
| indexOf(“hijklj”, “j” ) | 2 |
If you want the full credit, then it must also be able to complete the following example calls
| Method Call | return value/output |
| indexOf(“acxb”, “cx” ) | 1 |
| indexOf(“acxb”, “cxb” ) | 1 |
| indexOf(“acxb”, “cxbt” ) | -1 |
int countChars(String str, String chars)
@precondtion : chars.length() <= str.lenght()
Description: This method returns the number of times that chars occurs in String str .
| Method Call | return value/output |
| countChars(“momdadmom” , “dad” ) | 1 |
| countChars(“foobofoo” , “foo”) | 2 |
| countChars(“foobofoofoo” , “foo”) | 3 |
| countChars(“foobofoofoo” , “xy” ) | 0 |
Part II
String[] toArray(String str)
Description: This method returns an array comprised of the individual characters of str
| Method Call | return value/output |
| toArray(“abc” ) | { “a”, “b”, “c”} |
| toArray(“xyz” ) | {“x”, “y”, “z”} |
String[] toArraySansChar(String str, char ch)
Description: This method returns an array of Strings comprised of single letter strings extracted from the input String str ; however, we will always skip the char ch :
String[] reversedBy2s(String str)
Description: This method returns an array of Strings comprised of pairs of characters from the input, — in reverse order as shown below:
* boolean isPalindrome(String str)
Description: This method returns true if str is a palindrome.
| Method Call | return value/output |
| isPalindrome(“abc” ) | false |
| isPalindrome(“aba” ) | true |
| isPalindrome(“abba” ) | true |