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Answers to Questions and Exercises: Strings

Questions

1. Question: What is the initial capacity of the following string buffer?

   StringBuffer sb = new StringBuffer("Able was I ere I saw Elba.");
   

   Answer: It's the length of the initial string + 16: 26 + 16 = 42.
2. Consider the following string:

   String hannah = "Did Hannah see bees? Hannah did.";
   

   1. Question: What is the value displayed by the expression hannah.length()?
      Answer: 32.
   2. Question: What is the value returned by the method call hannah.charAt(12)?
      Answer: e.
   3. Question: Write an expression that refers to the letter b in the string referred to by hannah.
      Answer: hannah.charAt(15).
3. Question: How long is the string returned by the following expression? What is the string?

   "Was it a car or a cat I saw?".substring(9, 12)
   

   Answer: It's 3 characters in length: car. It does not include the space after car.
4. Question: In the following program, called ComputeResult, what is the value of result after each numbered line executes?

   public class ComputeResult {
       public static void main(String[] args) {
           String original = "software";
           StringBuffer result = new StringBuffer("hi");
           int index = original.indexOf('a');
   
   /*1*/   result.setCharAt(0, original.charAt(0));
   /*2*/   result.setCharAt(1, original.charAt(original.length()-1));
   /*3*/   result.insert(1, original.charAt(4));
   /*4*/   result.append(original.substring(1,4));
   /*5*/   result.insert(3, (original.substring(index, index+2) + " "));
   
           System.out.println(result);
       }
   }
   

   Answer:
   1. si
   2. se
   3. swe
   4. sweoft
   5. swear oft

Exercises

1. Exercise: Show two ways to concatenate the following two strings together to get the string "Hi, mom.":

   String hi = "Hi, ";
   String mom = "mom.";
   

   Solution: hi.concat(mom) and hi + mom.
2. Exercise: Write a program that computes your initials from your full name and displays them.
   Solution: ComputeInitials

   public class ComputeInitials {
       public static void main(String[] args) {
           String myName = "Fred F. Flintstone";
           StringBuffer myInitials = new StringBuffer();
           int length = myName.length();
   
           for (int i = 0; i < length; i++) {
               if (Character.isUpperCase(myName.charAt(i))) {
                   myInitials.append(myName.charAt(i));
               }
           }
           System.out.println("My initials are: " + myInitials);
       }
   }
   

3. Exercise: An anagram is a word or a phrase made by transposing the letters of another word or phrase; for example, "parliament" is an anagram of "partial men," and "software" is an anagram of "swear oft." Write a program that figures out whether one string is an anagram of another string. The program should ignore white space and punctuation.
   Solution: Anagram

    
   /** 
    * This class compiles with v 1.2 and 1.3, but not previous
    * versions, because its sort method uses the Arrays class,
    * which was added in 1.2.  To make Anagram work with early
    * versions of the Java platform, you need to reimplement
    * the sort method. 
    */
   
   public class Anagram {
   
       /**
        * Tests whether the passed-in strings are anagrams --
        * containing the exact same number of each letter.
        * Punctuation, case, and (obviously) order don't matter.
        * 
        * @return true if the strings are anagrams; otherwise, false
        */
       public static boolean areAnagrams(String string1,
                                         String string2) {
   
           String workingCopy1 = removeJunk(string1);
           String workingCopy2 = removeJunk(string2);
   
   	workingCopy1 = workingCopy1.toLowerCase();
   	workingCopy2 = workingCopy2.toLowerCase();
   
   	workingCopy1 = sort(workingCopy1);
   	workingCopy2 = sort(workingCopy2);
   
           return workingCopy1.equals(workingCopy2);
       }
   
       /**
        * Removes punctuation, spaces -- everything except letters
        * and digits from the passed-in string.
        * 
        * @return a stripped copy of the passed-in string
        */
       protected static String removeJunk(String string) {
           int i, len = string.length();
     	StringBuffer dest = new StringBuffer(len);
   	char c;
   
   	for (i = (len - 1); i >= 0; i--) {
   	    c = string.charAt(i);
   	    if (Character.isLetterOrDigit(c)) {
   		dest.append(c);
   	    }
   	}
   
           return dest.toString();
       }
   
       /** 
        * Sorts the passed-in string.  Reimplement this method
        * if you want to use this class in pre-Java-2 versions
        * of the platform.
        * 
        * @return a sorted copy of the passed-in string
        */
       protected static String sort(String string) {
   	int length = string.length();
           char[] charArray = new char[length];
   
   	string.getChars(0, length, charArray, 0);
   
   	//NOTE: The following line of code causes pre-1.2
   	//compilers to choke.
   	java.util.Arrays.sort(charArray);
   
           return new String(charArray);
       }
   
       public static void main(String[] args) {
           String string1 = "Cosmo and Laine:";
           String string2 = "Maid, clean soon!";
   
           System.out.println();
           System.out.println("Testing whether the following "
                            + "strings are anagrams:");
           System.out.println("    String 1: " + string1);
           System.out.println("    String 2: " + string2);
           System.out.println();
   
           if (areAnagrams(string1, string2)) {
               System.out.println("They ARE anagrams!");
           } else {
               System.out.println("They are NOT anagrams!");
           }
           System.out.println();
       }
   }
   

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