2016年AP计算机简答题真题PDF下载
1. This question involves the implementation and extension of a RandomStringChooser class.
(a) A RandomStringChooser object is constructed from an array of non-null String values. When the object is first constructed, all of the strings are considered available. The RandomStringChooser class has a getNext method, which has the following behavior. A call to getNext returns a randomly chosen string from the available strings in the object. Once a particular string has been returned from a call to getNext, it is no longer available to be returned from subsequent calls to getNext. If no strings are available to be returned, getNext returns "NONE".
The following code segment shows an example of the behavior of RandomStringChooser.
String[] wordArray = {"wheels", "on", "the", "bus"};
RandomStringChooser sChooser = new RandomStringChooser(wordArray);
for (int k = 0; k < 6; k++)
{System.out.print(sChooser.getNext() + " "); }
One possible output is shown below. Because sChooser has only four strings, the string "NONE" is printed twice.
bus the wheels on NONE NONE
Write the entire RandomStringChooser class. Your implementation must include an appropriate constructor and any necessary methods. Any instance variables must be private. The code segment in the example above should have the indicated behavior (that is, it must compile and produce a result like the possible output shown). Neither the constructor nor any of the methods should alter the parameter passed to the constructor, but your implementation may copy the contents of the array.
(b) The following partially completed RandomLetterChooser class is a subclass of the RandomStringChooser class. You will write the constructor for the RandomLetterChooser class.
public class RandomLetterChooser extends RandomStringChooser
{
/** Constructs a random letter chooser using the given string str.
* Precondition: str contains only letters.
*/
public RandomLetterChooser(String str)
{ /* to be implemented in part (b) */ }
/** Returns an array of single-letter strings.
* Each of these strings consists of a single letter from str. Element k
* of the returned array contains the single letter at position k of str.
* For example, getSingleLetters("cat") returns the
* array { "c", "a", "t" }.
*/
public static String[] getSingleLetters(String str)
{ /* implementation not shown */ }
}
The following code segment shows an example of using RandomLetterChooser.
RandomLetterChooser letterChooser = new RandomLetterChooser("cat");
for (int k = 0; k < 4; k++)
{
System.out.print(letterChooser.getNext());
}
The code segment will print the three letters in "cat" in one of the possible orders. Because there are only three letters in the original string, the code segment prints "NONE" the fourth time through the loop. One possible output is shown below.
actNONE
Assume that the RandomStringChooser class that you wrote in part (a) has been implemented correctly and that getSingleLetters works as specified. You must use getSingleLetters appropriately to receive full credit.
Complete the RandomLetterChooser constructor below.
/** Constructs a random letter chooser using the given string str.
* Precondition: str contains only letters.
*/
public RandomLetterChooser(String str)
2016年AP计算机简答题真题余下省略！
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