Arrays and Strings - Beginning Java - page 191

StringBuffer aString = new StringBuffer("A stitch in time");
You can add to it with the statement:
aString.append(" saves nine");
After this aString contains "A stitch in time saves nine" . The length of the string contained in the
StringBuffer object is increased by the length of the string that you add. You don't need to worry about
running out of space though. The capacity is always increased automatically whenever necessary to accom-
modate the longer string.
The append() method returns a reference to the extended StringBuffer object, so you could also assign
it to another StringBuffer object. Instead of the previous statement, you could have written:
StringBuffer bString = aString.append(" saves nine");
Now both aString and bString point to the same StringBuffer object.
If you take a look at the operator precedence table in Chapter 2, you see that the '.' operator (sometimes
called the member selection operator) that you use to execute a particular method for an object has left-to-
right associativity. You can therefore write multiple append operations in a single statement:
StringBuffer proverb = new StringBuffer(); // Capacity is 16
proverb.append("Many").append(" hands").append(" make").
append(" light").append(" work.");
The second statement is executed from left to right, so that the string contained in the object proverb is
progressively extended until it contains the complete string. The reference that each call to append() returns
is used to call append() again for the same object, proverb .
Appending a Substring
Another version of the append() method adds part of a String or a StringBuffer object to a
StringBuffer object. This version of append() requires three arguments: a reference to the String or
StringBuffer object from which the substring to be appended is obtained, the index position of the first
character in the object for the substring that is to be appended, and the index position of one past the last
character to be appended. If you supply null as the first argument, the substring from will be extracted from
the string "null" .
To illustrate the workings of this, suppose you create a StringBuffer object and a String object with
the following statements:
StringBuffer buf = new StringBuffer("Hard ");
String aString = "Waxworks";
You can then append part of the aString object to the buf object with this statement:
buf.append(aString, 3, 7);
This operation is shown in Figure 4-13 .
FIGURE 4-13