String Class

Summary

The String class represents a sequence of characters. In .NET, strings are immutable objects; once a string object is created, its value cannot be changed. Any operation that appears to modify a string actually creates a new string object.

Strings are fundamental data types in programming and are used extensively for text manipulation, data representation, and user interface elements. The String class provides a rich set of methods for working with strings, including operations such as concatenation, searching, replacing, splitting, and formatting.

Remarks

Strings in .NET are encoded using UTF-16. The String class is a reference type, but it is treated as a value type in many contexts, particularly with regard to its immutability.

The String class implements several interfaces, including ICloneable, IComparable, IConvertible, IEnumerable, and IList<Char>, providing a wide range of functionalities.

Fields

• Empty Represents an empty string.
• ordinals Internal field, do not use. (Note: This is a placeholder, actual internal fields might differ or not be publicly documented)

Constructors

• String(Char[], Int32, Int32) Initializes a new instance of the String class by using a specified array of Unicode characters, a starting position within that array, and the number of characters to use.
• String(Char[]) Initializes a new instance of the String class by using a specified array of Unicode characters.
• String(Char, Int32) Initializes a new instance of the String class to the specified number of occurrences of a character.

Methods

• Compare(String, String) Compares two strings, returning a value indicating whether one is less than, equal to, or greater than the other.
• Concat(Object[]) Concatenates the string representations of the elements in a specified array of objects.
• Contains(Char) Determines whether this string contains a specified character.
• EndsWith(String) Determines whether the end of this string instance matches the specified string.
• Equals(String) Determines whether the specified String object is equal to the current String object.
• Format(String, Object[]) Formats a string by using the specified format string and arguments.
• IndexOf(Char) Returns the zero-based index of the first occurrence of the specified Unicode character within this instance.
• IsNullOrEmpty(String) Indicates whether the specified string is null or an empty string.
• IsNullOrWhiteSpace(String) Indicates whether the specified string is null, empty, or consists only of white-space characters.
• Join(String, String[]) Concatenates the elements of a string array, using the specified separator between each element.
• get_Length() Gets the number of characters in the current String object.
• PadLeft(Int32) Pads the current string with spaces or a specified character, so that the resulting string reaches a specified length.
• Replace(Char, Char) Replaces all occurrences of a specified character in the current string with another specified character.
• Split(Char[]) Splits a string into substrings by separating the string at each character in a specified array of characters.
• StartsWith(String) Determines whether the beginning of this string instance matches the specified string.
• Substring(Int32) Retrieves a substring from this instance. The substring begins at a specified character position and continues to the end of the string.
• ToLower() Converts this string to lowercase.
• ToUpper() Converts this string to uppercase.
• Trim() Removes all leading and trailing white space characters from the current String object.

Properties

• Length Gets the number of characters in the current String object.
• Chars(Int32) Gets the character at the specified position in the current String object.

Example

The following example demonstrates common operations with the String class:

using System;

public class Example
{
    public static void Main()
    {
        // String declaration and initialization
        string greeting = "Hello";
        string name = "World";
        string message;

        // String concatenation
        message = String.Concat(greeting, ", ", name, "!");
        Console.WriteLine(message); // Output: Hello, World!

        // String formatting
        message = String.Format("The length of the message is: {0}", message.Length);
        Console.WriteLine(message); // Output: The length of the message is: 14

        // Checking if a string contains another string
        if (greeting.Contains("lo"))
        {
            Console.WriteLine("Greeting contains 'lo'."); // Output: Greeting contains 'lo'.
        }

        // Extracting a substring
        string sub = name.Substring(1, 3);
        Console.WriteLine(sub); // Output: orl

        // Converting to uppercase
        string upperGreeting = greeting.ToUpper();
        Console.WriteLine(upperGreeting); // Output: HELLO

        // Splitting a string
        string fruits = "Apple,Banana,Orange";
        string[] fruitArray = fruits.Split(',');
        Console.WriteLine("Fruits:");
        foreach (string fruit in fruitArray)
        {
            Console.WriteLine("- {0}", fruit);
        }
        // Output:
        // Fruits:
        // - Apple
        // - Banana
        // - Orange

        // Joining strings
        string joinedFruits = String.Join(" | ", fruitArray);
        Console.WriteLine(joinedFruits); // Output: Apple | Banana | Orange

        // Checking for null or empty
        string nullString = null;
        string emptyString = "";
        Console.WriteLine("Is nullString null or empty? {0}", String.IsNullOrEmpty(nullString)); // Output: True
        Console.WriteLine("Is emptyString null or empty? {0}", String.IsNullOrEmpty(emptyString)); // Output: True
        Console.WriteLine("Is greeting null or empty? {0}", String.IsNullOrEmpty(greeting)); // Output: False
    }
}