StringBuffer / StringBuilder

String and StringBuffer are two classes which extensively used in Java. As String is final in Java so it is immutable and once created cannot be changed whereas StringBuffer class is a mutable class. At a time String cannot be used by two threads.

Example :

               String Str = “Hello”;

               Then we concat a string value to the same string variable.

               Str = Str + ” Friend”;

When the value of 'Str' printed we get 'Hello Friends' but even we used same variable but a new object was created in the process when the  "Hello" string still exists but we lost the reference to it.

StringBuffer is mutable and one can change the value of the object because it is stored in the heap.

append() - Use for concatenation. Apart from a String, other data type also can be concatnate with StringBuffer. Also used for Array of characters.

Example:

               String Buffer Sb=new StringBuffer("Test");

               SB=SB.append(" Over");

               int x=10;

               SB=SB.append(x);

List of StringBuffer class: methods

capacity()	Returns the current capacity.
charAt(int)	Same as String.charAt(int)
delete(int Pos1, int Pos2)	Removes characters between given two points.
insert(int, String)	Insert a string at 's' position. This method can be applied for other data type too.
lastIndexOf(String)	Same as String.
replace(int, int, String)	Replace characters in a substring given String.
reverse()	Reverse the given String.
setCharAt(int, char)	Replace the character at the specified position with ch.
substring(int int)	Same as String.
substring(int)	Same as String.
indexOf(String)	Same as String.
indexOf(Stringr, int)	Same as String.
lastIndexOf(String, int)	Same as String.
length()	Same as String.
toString()	Same as String.

Some other Methods -

setLength(int newLength), subSequence(int, int), codePointAt(int),  ensureCapacity(int), getChars(int, int, char[], int), setLength(int), subSequence(int ,int), trimToSize()

StringBuilder

StringBuilder class too represents string objects and like StringBuffer it can be changed. StringBuilder also contains methods such as append, insert and can be use like one we have seen in StringBuffer. At the basic difference is the StringBuilder is faster than StringBuffer.

Almost all methods that used in StringBuufer can be used in StringBuilder too.

Example :

 StringBuilder str = new StringBuilder("Life is ");

 str = str.append(" is beautiful");

Now, it up to you, how you use your string.