Arrays and Strings - Beginning Java - page 195

There's another version of insert() that you can use to insert a substring of a String or StringBuffer
object into a StringBuffer object. The first argument is the offset index for the insertion; the second is the
reference to the source of the substring; the third argument is the index for the first character of the sub-
string; and the last argument is the index of one beyond the last character in the substring.
NOTE If you look in the JDK documentation for StringBuffer , you see parameters for
insert() and other methods of type CharSequence . This type allows a String or
StringBuffer reference to be supplied (as well as some other types). I avoid discussing
CharSequence further at this point because it is different from a class type and it needs an
in-depth explanation. I explain this in Chapter 6.
Extracting Characters from a Mutable String
The StringBuffer class includes the charAt() and getChars() methods, both of which work in the same
way as the methods of the same name in the String class which you've already seen. The charAt() method
extracts the character at a given index position, and the getChars() method extracts a range of characters
and stores them in an array of type char[] starting at a specified index position.
You should note that there is no equivalent to the getBytes() method for StringBuffer objects.
However you can obtain a String object from a CharBuffer object by calling its toString() method,
then you can call getBytes() for the String object to obtain the byte[] array corresponding to the
StringBuffer object.
Other Mutable String Operations
You can change a single character in a StringBuffer object by using the setCharAt() method. The first
argument indicates the index position of the character to be changed, and the second argument specifies the
replacement character. For example, the statement
buf.setCharAt(3, 'Z');
sets the fourth character in the string to 'Z' .
You use the deleteCharAt() method to remove a single character from a StringBuffer object at the
index position specified by the argument. For example:
StringBuffer phrase = new StringBuffer("When the boats come in");
phrase.deleteCharAt(10);
After these statements have executed, phrase contains the string "When the bats come in" .
If you want to remove several characters from a StringBuffer object you use the delete() method.
This method requires two arguments: The first is the index of the first character to be deleted, and the second
is the index position following the last character to be deleted. For example:
phrase.delete(5, 9);