STRINGS - Introduction to Java Programming - page 355

reverses the string in the builder and assigns the builder's reference to stringBuilder1 .
Thus, stringBuilder and stringBuilder1 both point to the same StringBuilder
object. Recall that a value-returning method can be invoked as a statement, if you are not
interested in the return value of the method. In this case, the return value is simply ignored.
For example, in the following statement

stringBuilder.reverse();

the return value is ignored.

Tip
If a string does not require any change, use String rather than StringBuilder . Java
can perform some optimizations for String , such as sharing interned strings.

String or StringBuilder ?

9.6.2 The toString , capacity , length , setLength ,
and charAt Methods
The StringBuilder class provides the additional methods for manipulating a string builder
and obtaining its properties, as shown in Figure 9.13.

java.lang.StringBuilder

+toString(): String
+capacity(): int
+charAt(index: int): char
+length(): int
+setLength(newLength: int): void
+substring(startIndex: int): String
+substring(startIndex: int, endIndex: int):
String
+trimToSize(): void

Returns a string object from the string builder.
Returns the capacity of this string builder.
Returns the character at the specified index.
Returns the number of characters in this builder.
Sets a new length in this builder.
Returns a substring starting at startIndex .
Returns a substring from startIndex to endIndex-1 .

Reduces the storage size used for the string builder.

F IGURE 9.13

The StringBuilder class contains the methods for modifying string builders.

The capacity() method returns the current capacity of the string builder. The capacity is
the number of characters the string builder is able to store without having to increase its size.
The length() method returns the number of characters actually stored in the string
builder. The setLength(newLength) method sets the length of the string builder. If the
newLength argument is less than the current length of the string builder, the string builder is
truncated to contain exactly the number of characters given by the newLength argument. If
the newLength argument is greater than or equal to the current length, sufficient null charac-
ters ( \u0000 ) are appended to the string builder so that length becomes the newLength
argument. The newLength argument must be greater than or equal to 0 .
The charAt(index) method returns the character at a specific index in the string
builder. The index is 0 based. The first character of a string builder is at index 0 , the next at
index 1 , and so on. The index argument must be greater than or equal to 0 , and less than the
length of the string builder.

capacity()

length()
setLength(int)

charAt(int)

Note
The length of the string is always less than or equal to the capacity of the builder. The
length is the actual size of the string stored in the builder, and the capacity is the current
size of the builder. The builder's capacity is automatically increased if more characters
are added to exceed its capacity. Internally, a string builder is an array of characters, so

length and capacity