



StringBuffer Class


An instance of Java's StringBuffer class represents a string that can be
dynamically modified. These are the constructors:

StringBuffer()  This constructs an empty string buffer

StringBuffer(int capacity)  This constructs an empty string
buffer with the specified initial capacity.

StringBuffer(String initialString) This constructs a 
string buffer that initially contains the specified string.

StringBuffer Methods:


StringBuffer append(String str) This appends str to the current
string buffer. Alternative forms support appending primitives and character
arrays; these are converted to strings before appending.

StringBuffer append(Object obj) This calls toString() on obj
and appends the result to the current string buffer.

StringBuffer insert(int offset, String str) This inserts str
into the current string buffer at position offset. There are numerous alternative 
forms.

StringBuffer reverse() This reverses the characters of the
current string buffer.

StringBuffer setCharAt(int offset, char newchar) This
replaces the character at position offset with newchar.

StringBuffer setLengthInit newLength) This sets the length
of the string buffer to newLength. If newLength is less than the current
length, the string is truncated. If newLength is greater than the current
length, the string is padded with null characters.




StringBuffer In Action: Here's a short example program showing
a few StringBuffer methods in action:

class buf{
  public static void main(String[]args) {
    StringBuffer sb = new StringBuffer("12345");
    prt(sb);
    sb.reverse();
    prt(sb);
    sb.insert(3,"abcde");
    prt(sb);
    sb.append("xyz");
    prt(sb);
  }
  static void prt(StringBuffer s) {
    System.out.println(s);
  }
}





Sample Assignment: This might be a difficult project. You will create
an application which scrambles words. The user will enter a word as an
argument and indicate a scrambling method. The easiest way to indicate a scrambling
method is with a 1, 2, or 3 since there are just three methods.
Here are the three methods you must implement for this assignment:


Method Brief Description Example

1 reverse, store, truncate, insert
input: carpet

step one: teprac

step two: store last half of word (rac) 

step three: truncate last half of word

step four: insert stored part (rac) infront of first part (tep)

result: ractep

2 pick random letter and alternately insert in front of it and
concat after it
input: carpet

step one: pick random letter: (a) store it and delete it from input

step two: insert first letter from input infront of stored letter: ca

step three: concatenate next letter at end: car

repeat insert/concatenate: pcar, pcare, tpcare.

result: tpcare (actual results will vary since first letter is selected at
random).

3 store, truncate, random insert four times
input: carpet

step one: store last letter (t), truncate last letter, randomly insert

possible result to step one: catrpe

step two: store last letter (e), truncate last letter, randomly insert

possible result to step two: caetrp

step three: store last letter (p), truncate last letter, randomly insert

possible result to step three: caetpr

step four: store last letter (r), truncate last letter, randomly insert

possible result to step four: caretp

result: caretp (actual results will vary since the four insertions are made
into randomly selected positions)


Basically, you will have a case statement which is used to route a call to
one of these three methods. Each of these methods must return a String.

StringBuffer()	This constructs an empty string buffer
StringBuffer(int capacity)	This constructs an empty string buffer with the specified initial capacity.
StringBuffer(String initialString)	This constructs a string buffer that initially contains the specified string.

StringBuffer append(String str)	This appends str to the current string buffer. Alternative forms support appending primitives and character arrays; these are converted to strings before appending.
StringBuffer append(Object obj)	This calls toString() on obj and appends the result to the current string buffer.
StringBuffer insert(int offset, String str)	This inserts str into the current string buffer at position offset. There are numerous alternative forms.
StringBuffer reverse()	This reverses the characters of the current string buffer.
StringBuffer setCharAt(int offset, char newchar)	This replaces the character at position offset with newchar.
StringBuffer setLengthInit newLength)	This sets the length of the string buffer to newLength. If newLength is less than the current length, the string is truncated. If newLength is greater than the current length, the string is padded with null characters.

Method	Brief Description	Example
1	reverse, store, truncate, insert	input: carpet step one: teprac step two: store last half of word (rac) step three: truncate last half of word step four: insert stored part (rac) infront of first part (tep) result: ractep
2	pick random letter and alternately insert in front of it and concat after it	input: carpet step one: pick random letter: (a) store it and delete it from input step two: insert first letter from input infront of stored letter: ca step three: concatenate next letter at end: car repeat insert/concatenate: pcar, pcare, tpcare. result: tpcare (actual results will vary since first letter is selected at random).
3	store, truncate, random insert four times	input: carpet step one: store last letter (t), truncate last letter, randomly insert possible result to step one: catrpe step two: store last letter (e), truncate last letter, randomly insert possible result to step two: caetrp step three: store last letter (p), truncate last letter, randomly insert possible result to step three: caetpr step four: store last letter (r), truncate last letter, randomly insert possible result to step four: caretp result: caretp (actual results will vary since the four insertions are made into randomly selected positions)