StringBuffer:

As we know in Java String is immutable means we cannot reassign a new value to the same string object. That's why in Java to provide mutability we use either StringBuffer or StringBuilder. StringBuffer is a class in Java which provide mutability as we can modify the string object value.

StringBuffer constructors:

 StringBuffer() // It creates an empty string buffer with capacity of 16.
 StringBuffer(String str)// It creates a string buffer with string provided.
 StringBuffer(int capacity)

Some of the methods of StringBuffer:

1.append():

It is used to add some arguments with the string.

Example:

class Buffer{  
public static void main(String args[]){  
StringBuffer obj=new StringBuffer("Welcome ");  
obj.append("to FindNerd");//appending more characters to string  
System.out.println(obj); //prints Welcome to FindNerd
}  
}  

2. reverse():

It reverses the string on which reverse method will be used.

Example:

   class Buffer{  
    public static void main(String args[]){  
    StringBuffer obj=new StringBuffer("Welcome ");  
   obj.reverse();  
   System.out.println(obj);//prints emocleW  
}  
}  

3.insert():

This method is used to insert string provided at a particular index.

Example:

class Buffer{  
    public static void main(String args[]){  
    StringBuffer obj=new StringBuffer("Welcome ");  
    obj.insert(1,"Java");//now original string is changed  
    System.out.println(obj);//prints WJavaelcome  
    }  
    }  

4. replace():

It replaces string from the specified StartingIndex and EndIndex.