What is StringBuilder Class ?

The StringBuilder class is used to created mutable (modifiable) string.The StringBuilder class is same as StringBuilder class except that it is non-synchronized. It is available since JDK1.5.

Note: StringBuilder class is not a thread-safe means multiple threads can access it simultaneously. So a proper order while acccessing by multiple thread is not maintain.

Commonly used Constructors of StringBuilder class:

>1. StringBuilder(): creates an empty string buffer with the initial capacity of 16.
>2. StringBuilder(String str): creates a string buffer with the specified string.
>3. StringBuilder(int capacity): creates an empty string buffer with the specified capacity as length.


Commonly used methods of StringBuider class:



>1. public synchronized StringBuilder append(String s): is used to append the specified string              with this string. The append() method is overloaded like append(char), append(boolean),                      append(int), append(float), append(double) etc.
>2. public synchronized StringBuilder insert(int offset, String s): is used to insert the specified            string with this string at the specified position. The insert() method is overloaded like
      insert(int, char), insert(int, boolean), insert(int, int), insert(int, float), insert(int, double) etc.
>3. public synchronized StringBuilder replace(int startIndex, int endIndex, String str): is used         to replace the string from specified startIndex and endIndex.
>4. public synchronized StringBuilderdelete(int startIndex, int endIndex): is used to delete the
      string from specified startIndex and endIndex.
>5. public synchronized StringBuilder reverse(): is used to reverse the string.
>6. public int capacity(): is used to return the current capacity.
>7. public void ensureCapacity(int minimumCapacity): is used to ensure the capacity at least              equal to the given minimum.
>8. public char charAt(int index): is used to return the character at the specified position.
>9. public int length(): is used to return the length of the string i.e. total number of characters.
>10. public String substring(int beginIndex): is used to return the substring from the specified
       beginIndex.
>11. public String substring(int beginIndex, int endIndex): is used to return the substring from the
     specified beginIndex and endIndex.

An example of StringBuilder class by append() method:

The append() method concatenates the given argument with this string.

class Test{
public static void main(String args[]){
StringBuilder sb=new StringBuilder("vishwa ");
sb.append("welcome");
System.out.println(sb);
   }
}

Output: vishwa welcome

Example of insert() method of StringBuilder class:

The insert() method inserts the given string with this string at the given position.

class Test{
public static void main(String []args){
StringBuilder sb=new StringBuilder("vishwa ");
sb.insert(2,"hello");
System.out.println(sb);
   }
}

Output: vihelloshwa

Example of replace() method of StringBuilder class:

The replace() method replaces the given string from the specified beginIndex(inclusive) and endIndex(exclusive).

class Test{
public static void main(String []args){
StringBuilder sb=new StringBuilder("vishwa");
sb.replace(1,4,"hello");
System.out.println(sb);
   }
}

Output:vhellowa



Example of delete() method of StringBuilder class:

The delete() method of StringBuilder class deletes the string from the specified beginIndex to endIndex.

class Test{
public static void main(String []args){
StringBuilder sb=new StringBuilder("vishwa");
sb.delete(1,4);
System.out.println(sb);
  }
}


Output: vwa

Example of reverse() method of StringBuilder class:

The reverse() method of StringBuilder class reverses the current string.

class Test{
public static void main(String []args){
StringBuilder sb=new StringBuilder("vishwa");
sb.reverse();
System.out.println(sb);
   }
}

Output: awhsiv

Example of capacity() method of StringBuilder class:

The capacity() method of StringBuilder class returns the current capacity of the buffer.The default capacity of the buffer is 16.
If the number of character increases from its current capacity, it increases the capacity by (oldcapacity*2)+2. For example if your  current capacity is 16, it will be (16*2)+2=34.

class Test{
public static void main(String []args){

StringBuildersb=new StringBuilder();
System.out.println(sb.capacity());
sb.append("vishwa");
System.out.println(sb.capacity());
sb.append("my name is vishwa");
System.out.println(sb.capacity());
   }
}

Output:  16  (by default)
                16
                34