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C# | Collection Class

  • Last Updated : 01 Feb, 2019
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Collection<T> Class provides the base class for a generic collection. Here T is the type of elements in the collection. This class comes under the System.Collections.ObjectModel namespace.

Characteristics:

  • The Collection<T> class can be used immediately by creating an instance of one of its constructed types.
  • The Collection<T> class provides protected methods that can be used to customize its behavior when adding and removing items, clearing the collection, or setting the value of an existing item.
  • Most Collection<T> objects can be modified. However, a Collection object that is initialized with a read-only IList<T> object cannot be modified.
  • Elements in this collection can be accessed using an integer index. Indexes in this collection are zero-based.
  • Collection<T> accepts null as a valid value for reference types and allows duplicate elements.

Constructors

ConstructorDescription
Collection<T>()Initializes a new instance of the Collection<T> class that is empty.
Collection<T>(IList<T>)Initializes a new instance of the Collection<T> class as a wrapper for the specified list.

Example:




// C# code to create a Collection
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
        // Creating a collection of ints
        Collection<int> myColl = new Collection<int>();
  
        // Adding elements in Collection myColl
        myColl.Add(2);
        myColl.Add(3);
        myColl.Add(4);
        myColl.Add(5);
  
        // Displaying the elements in myColl
        foreach(int i in myColl)
        {
            Console.WriteLine(i);
        }
    }
}

Output:

2
3
4
5

Properties

PropertyDescription
CountGets the number of elements actually contained in the Collection<T>.
ItemsGets a IList<T> wrapper around the Collection<T>.
Item[Int32]Gets or sets the element at the specified index.

Example:






// C# Code to illustrate the 
// Properties of Collection class
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
   
class GFG {
   
    // Driver code
    public static void Main()
    {
          
        // Creating a collection of strings
        Collection<string> myColl = new Collection<string>();
   
        // Adding elements in Collection myColl
        myColl.Add("A");
        myColl.Add("B");
        myColl.Add("C");
        myColl.Add("D");
        myColl.Add("E");
          
        // ------- Count Property ----------
          
        // To print the count of
        // elements in Collection
        Console.WriteLine("Count : " + myColl.Count);
   
        // -------- Item[Int32] Property --------
          
        // Get the element at index 2
        Console.WriteLine("Element at index 2 is : " + myColl[2]);
   
        // Get the element at index 3
        Console.WriteLine("Element at index 3 is : " + myColl[3]);
    }
}

Output:

Count : 5
Element at index 2 is : C
Element at index 3 is : D

Methods

MethodDescription
Add(T)Adds an object to the end of the Collection<T>.
Clear()Removes all elements from the Collection<T>.
ClearItems()Removes all elements from the Collection<T>.
Contains(T)Determines whether an element is in the Collection<T>.
CopyTo(T[], Int32)Copies the entire Collection<T> to a compatible one-dimensional Array, starting at the specified index of the target array.
Equals(Object)Determines whether the specified object is equal to the current object.
GetEnumerator()Returns an enumerator that iterates through the Collection<T>.
GetHashCode()Serves as the default hash function.
GetType()Gets the Type of the current instance.
IndexOf(T)Searches for the specified object and returns the zero-based index of the first occurrence within the entire Collection<T>.
Insert(Int32, T)Inserts an element into the Collection<T> at the specified index.
InsertItem(Int32, T)Inserts an element into the Collection at the specified index.
MemberwiseClone()Creates a shallow copy of the current Object.
Remove(T)Removes the first occurrence of a specific object from the Collection<T>.
RemoveAt(Int32)Removes the element at the specified index of the Collection<T>.
RemoveItem(Int32)Removes the element at the specified index of the Collection<T>.
SetItem(Int32, T)Replaces the element at the specified index.
ToString()Returns a string that represents the current object.

Example:




// C# code to check if an
// element is in the Collection
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
        // Creating a collection of strings
        Collection<string> myColl = new Collection<string>();
  
        myColl.Add("A");
        myColl.Add("B");
        myColl.Add("C");
        myColl.Add("D");
        myColl.Add("E");
  
        // Checking if an element is in the Collection
        // The function returns "True" if the
        // item is present in Collection
        // else returns "False"
        Console.WriteLine(myColl.Contains("A"));
    }
}

Output:

True

Example 2:




// C# code to copy the entire Collection
// to a compatible one-dimensional Array,
// starting at the specified index of
// the target array
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
  
class GFG {
  
    // Driver code
    public static void Main()
    {
        // Creating a collection of strings
        Collection<string> myColl = new Collection<string>();
  
        myColl.Add("A");
        myColl.Add("B");
        myColl.Add("C");
        myColl.Add("D");
        myColl.Add("E");
  
        // Creating a string array
        string[] myArr = new string[myColl.Count];
  
        // Copying the entire Collection to a
        // compatible one-dimensional Array,
        // starting at the specified index
        // of the target array
        myColl.CopyTo(myArr, 0);
  
        // Displaying the elements in myArr
        foreach(string str in myArr)
        {
            Console.WriteLine(str);
        }
    }
}

Output:

A
B
C
D
E

Reference:




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