The StringBuilder Class

The StringBuilder class is provided in the System.Text namespace to create an object that can hold a string value that can be changed. An object created with the StringBuilder class operates similarly to a string. The difference is that methods of a StringBuilder can directly manipulate the value stored. The methods and properties for a StringBuilder object are listed in table given below.

Table :The StringBuilder Methods and Properties

Methods or Properties                        Description

Append:                                 Appends an object to the end of the current StringBuilder. AppendFormat:                    Inserts objects into a string base on formatting specifiers. Capacity:                                Sets or gets the number of characters that can be held. Capacity can be increased up to the value of MaxCapacity. Chars:                                     Sets or gets the character at a given index position using indexer notation. EnsureCapacity:                    Ensures that the capacity of StringBuilder is at least as big as a provided Value:                                     If the value is passed to EnsureCapacity, the value of the Capacity property is set to this new value. If MaxCapacity is less than the value passed, an exception is thrown. Equals:                                   Determines whether the current StringBuilder is equal to the value passed. Insert:                                    Places an object into StringBuilder at a given location. Length:                                   Sets or gets the length of the current value stored in StringBuilder. Length cannot be larger than the Capacity of StringBuilder. If the current value is shorter than Length, the value is truncated. MaxCapacity:                        Gets the maximum capacity for StringBuilder. Remove:                                 Removes a specified number of characters, starting at a specified location within the current StringBuilder object. Replace:                                 Changes all copies of a given character with a new character. ToString:                               Converts StringBuilder to String.

The StringBuilder class can be used like other classes. The following program uses the StringBuilder object and several of the methods and properties presented in above table. This program has a user enter first, last, and middle names. The values are combined into a StringBuilder object.

The StringBuilder class is used to represent mutable strings. It starts at a predefined size (16 characters by default) and grows dynamically as more string data is added. It can either grow unbounded or up to a configurable maximum. For example:

=== Program that uses Replace () and Append () ===

using System;

using System.Text;

class Program

{

    static void Main()

    {

        StringBuilder builder = new StringBuilder("This is an example string");

        builder.Replace("an", "the"); // Replaces 'an' with 'the'.

        Console.WriteLine(builder);

        builder.Append(" that is an example.");

        Console.WriteLine(builder);

        

    }

}

=== Output of the program ===

This is the example string

This is the example string that is an example

=== Program that uses AppendFormat () ===

using System;

using System.Text;

class Program

{

    static int[] sb = new int[]{1,4,6};

   

    static void Main()

    {

        StringBuilder b = new StringBuilder();

        foreach (int i in sb)

        {

            b.AppendFormat("int: {0:0.0}\n",i);

        }

        Console.WriteLine(b.ToString());

    }

}

 

=== Output of the program ===

int: 1.0

int: 4.0

int: 6.0

=== using Remove () ===

 StringBuilder st = new StringBuilder("Football");

 st.Remove(4, 4);//Remove(int StartIndex,int length).

 Console.WriteLine(st);//Foot

=== using Insert () ===

StringBuilder st = new StringBuilder("Foot");

st.Insert(4, "ball");

Console.WriteLine(st);//Football

=== using Equals () ===

StringBuilder sb = new StringBuilder("c#");

StringBuilder sb1 = new StringBuilder("c#");

bool b= sb.Equals(sb1);

Console.WriteLine(b);//True

The chief advantage of a StringBuilder object over a string object is that it preallocates a default initial amount of memory in an internal buffer in which a string value can expand and contract. When that memory is used, however, .NET must allocate new memory for this internal buffer. You can reduce the frequency with which this occurs by explicitly defining the size of the new memory using either of two techniques. The first approach is to set this value when the StringBuilder class constructor is called. For example, the code:

        StringBuilder sb = new StringBuilder(200);

specifies that a StringBuilder object can hold 200 characters before new memory must be allocated.

The second approach is to change the value after the StringBuilder object has been created, using one of the following properties or methods of the StringBuilder object:

        sb.Capacity = 200;

        sb.EnsureCapacity(200);