STRINGS - Introduction to Java Programming - page 357

27 return s2.equals(s1);

28 }
29
30 /** Create a new string by eliminating nonalphanumeric chars */

31 public static String filter(String s) {

32 // Create a string builder

33
34
35

StringBuilder stringBuilder = new StringBuilder();

// Examine each char in the string to skip alphanumeric char

s.length()

36 for ( int i = 0 ; i < ; i++) {

37 if ( Character.isLetterOrDigit(s.charAt(i)) ) {

stringBuilder.append(s.charAt(i));

38
39 }
40 }
41
42

add letter or digit

// Return a new filtered string

43 return stringBuilder.toString();

44 }
45
46 /** Create a new string by reversing a specified string */
47 public static String reverse(String s) {
48 StringBuilder stringBuilder = new StringBuilder(s);
49 stringBuilder.reverse(); // Invoke reverse in StringBuilder

50 return stringBuilder.toString();

51 }
52 }

Enter a string:
Ignoring nonalphanumeric characters,
is ab<c>cb?a a palindrome? true

ab<c>cb?a

Enter a string:
Ignoring nonalphanumeric characters,
is abcc><?cab a palindrome? false

abcc><?cab

The filter(String s) method (lines 31-44) examines each character in string s and
copies it to a string builder if the character is a letter or a numeric character. The filter
method returns the string in the builder. The reverse(String s) method (lines 47-51) cre-
ates a new string that reverses the specified string s . The filter and reverse methods both
return a new string. The original string is not changed.
The program in Listing 9.1 checks whether a string is a palindrome by comparing pairs of
characters from both ends of the string. Listing 9.4 uses the reverse method in the
StringBuilder class to reverse the string, then compares whether the two strings are equal
to determine whether the original string is a palindrome.

9.15

✓ ✓

What is the difference between StringBuilder and StringBuffer ?

Check

9.16

How do you create a string builder from a string? How do you return a string from a
string builder?

Point

9.17

Write three statements to reverse a string s using the reverse method in the
StringBuilder class.

9.18

Write three statements to delete a substring from a string s of 20 characters, starting
at index 4 and ending with index 10 . Use the delete method in the

StringBuilder class.

9.19

What is the internal storage for characters in a string and a string builder?