STRINGS - Introduction to Java Programming - page 353

public static int m(String s) {
int count = 0 ;
for ( int i = 0 ; i < s.length(); i++)
if (Character.isUpperCase(s.charAt(i)))
count++;

return count;

}

}

9.6 The StringBuilder and StringBuffer Classes
The StringBuilder and StringBuffer classes are similar to the String class
except that the String class is immutable.

Key
Point

In general, the StringBuilder and StringBuffer classes can be used wherever a string is
used. StringBuilder and StringBuffer are more flexible than String . You can add,
insert, or append new contents into StringBuilder and StringBuffer objects, whereas
the value of a String object is fixed once the string is created.
The StringBuilder class is similar to StringBuffer except that the methods for modify-
ing the buffer in StringBuffer are synchronized , which means that only one task is allowed to
execute the methods. Use StringBuffer if the class might be accessed by multiple tasks con-
currently. Concurrent programming will be introduced in Chapter 32. Using StringBuilder is
more efficient if it is accessed by just a single task. The constructors and methods in
StringBuffer and StringBuilder are almost the same. This section covers
StringBuilder . You can replace StringBuilder in all occurrences in this section by
StringBuffer . The program can compile and run without any other changes.
The StringBuilder class has three constructors and more than 30 methods for manag-
ing the builder and modifying strings in the builder. You can create an empty string builder or
a string builder from a string using the constructors, as shown in Figure 9.11.

StringBuilder

StringBuilder
constructors

java.lang.StringBuilder

+StringBuilder()
+StringBuilder(capacity: int)
+StringBuilder(s: String)

Constructs an empty string builder with capacity 16 .
Constructs a string builder with the specified capacity.
Constructs a string builder with the specified string.

F IGURE 9.11 The StringBuilder class contains the constructors for creating instances of
StringBuilder .

9.6.1 Modifying Strings in the StringBuilder
You can append new contents at the end of a string builder, insert new contents at a specified
position in a string builder, and delete or replace characters in a string builder, using the meth-
ods listed in Figure 9.12.
The StringBuilder class provides several overloaded methods to append boolean ,
char , char[] , double , float , int , long , and String into a string builder. For example,
the following code appends strings and characters into stringBuilder to form a new string,
Welcome to Java .

StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append( "Welcome" );
stringBuilder.append( ' ' );
stringBuilder.append( "to" );
stringBuilder.append( ' ' );
stringBuilder.append( "Java" );

append