Exercises for String 1 and Array 1 (no loops)
When you are done, you can copy and past the score() method below into your class. It will test some (but, by no means all) of the things that your code should do
Create a class called StrArr1 and add each method below into it.
For the absVals() method below use the Math.abs() Java method.
For the randos1to10() method below use the Math.random() Java method. Create a new array to store random integers. Each integer should be [1,10]
Write the body for the methods described below.
Tester File here (This one does not yet test the newest method)
As always, do not import any external libraries. All of the coding can be accomplished by using just loops, arrays, strings and variables. Using anything else will lead to total loss of credit on associated methods.
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. Note: This does not test all the methods. I have added new methods since writing that tester file. Also, please make sure that:
boolean isAfterN(String str, String chrs, int index)
Description: This method returns true if chrs appears in str after index .
@precondition: index + chrs.length() < str.length()
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. Just to avoid any confusion – you cannot make use of the String’s built in indexOf() method. Our method returns the index of the 1st occurrence of needle in haystack . (Full credit if you can get this to work with Strings whose length is greater than 1).
int countChars(String str, String chars)
@precondtion : chars.length() <= str.length()
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 |
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 :
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1 2 |
char c = '3'; String s = String.valueOf(c); |
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:
String reverseBy3s(String str)
Description: This is like the prior method, except you are going by 3’s and returning a String , not an array of Strings.
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 |
Create a class called BaseMaster (spelled exactly like this)
//helper functions
the isNumeric() method returns true if every digit is an integer . It also allows for a single ‘.’ to represent a decimal point.
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1 2 3 4 |
//@returns true if input represents a valid integer or floating point number public boolean isNumeric(String in){ } |
|
1 2 3 4 5 |
//@returns input in base 'baseOut' //@precondition isNumeric(input) = true public String base10toOtherBase(String input, String baseOut){ } |
| example call | return value |
| isNumeric("3.1") | true |
| isNumeric("3.1.1") | false |
| isNumeric("3a") | true (assume base 16) |
| isNumeric("3D") | true (assume base 16) |
To get A+, you need to make base10toOtherBase() support bases 2-10 AND base 16
public int countF(String str)
Description: This method returns the number of times that the letter ‘f’ occurs in str.
| Method Call | return value/output |
| countF(“abcdef”) | 1 |
| countF(“abcdfef”) | 2 |
| countF(“fff”) | 3 |
| countF(“xxx”) | 0 |
public boolean has2Fs(String str)
Description: This method returns true if str has exactly two occurrences of the letter ‘f’ in it.
| Method Call | return value/output |
| has2Fs(“foo”) | false |
| has2Fs(“fofo”) | true |
| has2Fs(“foffo”) | false |
public boolean has2Fs3Gs(String str)
Description: This method returns true if str has exactly two occurrences of the letter ‘f’ in it and 3 occurences ‘g’.
| Method Call | return value/output |
| has2Fs3Gs(“foog”) | false |
| has2Fs3Gs(“foggfog”) | true |
| has2Fs3Gs(“foffoggg”) | false |
public int momOrDad(String str)
Description: This method returns the number of times that the String “mom” or the string “dad” occurs in the parameter str .
| Method Call | return value/output |
| momOrDad(“foog”) | 0 |
| momOrDad(“momf”) | 1 |
| momOrDad(“momdadmo”) | 2 |
| momOrDad(“momdadmom”) | 3 |
public 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(“”) | “” |
public 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” |
public String 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 |
public int indexOf(String haystack, String needle)
Description: Write your own indexOf() method. Obviously, you cannot make use of the String’s build 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 extra 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 |
public int countChars(String str, String chars)
Precondition:The length of chars is less than or equal to the length of str
Description: This method returns the number of times that charsoccurs in String str.
| Method Call | return value/output |
| countChars(“momdadmom” , “dad” ) | 1 |
| countChars(“foobofoo” , “foo”) | 2 |
| countChars(“foobofoofoo” , “foo”) | 3 |
| countChars(“foobofoofoo” , “xy” ) | 0 |