API Contents - SCJP Sun Certified Programmer for Java Platform SE6 - page 279

FIGURE 4.2 The sequence of characters increases by one each time through the loop.

alpha

String Builder object

'a' 'b' 'c' 'd' 'e' . . .

alpha.append ('e') j

The output of the code is

abcdefghijklmnopqrstuvwxyz

The principal methods of the StringBuilder and StringBuffer classes are their append
and insert methods. The append and insert methods are overloaded to accept any of the
primitive types, Object , String , or StringBuffer . To demonstrate the method signatures, here
are the append and insert methods in StringBuilder for appending and inserting a float :
public StringBuilder append(float f) appends the given float to the end of the
character sequence.
public StringBuilder insert(int offset, float f) inserts the given float at the
value of the offset. The first index of the sequence is 0, the second index is 1, and so on.

The overloaded methods for the other data types take on the same form as the methods
above. The append and insert methods are identical in StringBuffer , except that the
return values are of type StringBuffer :
public StringBuffer append(float f)
public StringBuffer insert(int offset, float f)
The append method appends the data to the end of the character sequence, while the
insert method inserts the data at the given offset. Notice that the return value of append
and insert is the original StringBuilder or StringBuffer object, which allows for the
chaining of method calls. For example, see if you can fi gure out the character sequence that
the following code generates:

24. StringBuffer sb = new StringBuffer();
25. sb.append(“cet”).insert(2,”ntra”).insert(0,”con”).append(“ing”);
26. System.out.println(sb);

Let's break this code down step by step:
1. The initial StringBuffer object instantiated on line 24 is empty.
2. On line 25, the methods are executed left to right, so the first append call puts ”cet”
in the sequence.