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]
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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//@returns true if input represents a valid integer or floating point number public boolean isNumeric(String in){ } |
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//@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 |