Module: AP Computer Science Section II 2015


Problem

3/4

strings

Problem

A text-editing program uses a Sentence class that manipulates a single sentence. A sentence contains letters, blanks, and punctuation. The first character in a sentence is a letter, and the last character is a punctuation mark. Any two words in the sentence are separated by a single blank. A partial implementation of the Sentence class is as follows.

a) Write the Sentencemethod getBlankPositions,which returns an ArrayList of integers that represent the positions in a sentence containing blanks. If there are no blanks in the sentence, getBlankPositions should return an empty list. Some results of calling getBlankPositions are shown below.


Complete method getBlankPositions below.
/** @return an ArrayList of integer positions containing a
* blank in this sentence. If there are no blanks in the
* sentence, returns an empty list.
*/
public List<Integer> getBlankPositions()
 
b) Write the Sentencemethod countWords,which returns the number of words in a sentence. Words are sequences of letters or punctuation, separated by a single blank. You may assume that every sentence contains at least one word.
For example:

Complete method countWords below.

/** @return the number of words in this sentence
* Precondition: Sentence contains at least one word.
*/
public int countWords()
 
c) Write the Sentence method getWords, which returns an array of words in the sentence. A word is defined as a string of letters and punctuation, and does not contain any blanks. You may assume that a sentence contains at least one word.
Some examples of calling getWords are shown below.

In writing method getWords, you must use methods getBlankPositions and countWords, which were written in parts (a) and (b). You may assume
that these methods work correctly, irrespective of what you wrote in parts (a) and (b).
Complete method getWords below.

/** @return the array of words in this sentence
* Precondition:
* - Any two words in the sentence are separated by one blank.
* - The sentence contains at least one word.
* Postcondition: String[] returned containing the words in
* this sentence.
*/
public String[] getWords()

 

time 1000 ms
memory 256 Mb
Rules for program design and list of errors in automatic problem checking

Teacher commentary

Insert the missing code snippets
Java
Write the program below 
import java.io.*;
import java.util.*;

public class Main
{
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String s = in.nextLine(); 
        Sentence sec = new Sentence(s);
        List<Integer> arr =  sec.getBlankPositions();
        for (Integer a: arr) {
            System.out.print(a+" ");
        }
        int count = sec.countWords();
        System.out.println();
        System.out.println(count);
        String[] b = sec.getWords();
        for (String a: b) {
            System.out.print(a);
        }
    }
}
 class Sentence
{
 public Sentence(String s)
    {
        sentence = s;   
    }
    /** The sentence to manipulate */
    private String sentence;
    /** @return an ArrayList of integer positions containing a
     * blank in this sentence. If there are no blanks in the
     * sentence, returns an empty list.
     */
    public List<Integer> getBlankPositions()
    { /* to be implemented in part (a) */            
}
 /** @return the number of words in this sentence
     * Precondition: Sentence contains at least one word.
     */
 public int countWords()
 { /* to be implemented in part (b) */            
}
 /** @return the array of words in this sentence
     * Precondition:
     * - Any two words in the sentence are separated by one blank.
     * - The sentence contains at least one word.
     * Postcondition: String[] returned containing the words in
     * this sentence.
     */
    public String[] getWords()
    { /* to be implemented in part (c) */            
}}

     

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