C# basic knowledge compilation: basic knowledge (15) ICollection, iteration and generics

1. ICollection interface
Array is the most basic collection type defined by .net framework. In addition to arrays, .net framework also defines many collection types. Open msdn and you can see that all collections are under the System.Collections namespace:
Collection class:
ArrayList: Implement the IList interface using an array whose size can be dynamically increased on demand.
BitArray: A compressed array that manages the value. The value is expressed as a Boolean value. true indicates that the bit is on (1), and false indicates that the bit is off (0).
CaseInsensitiveComparer: Compares two objects for equality, ignoring the case of strings when comparing.
CollectionBase: Provides an abstract base class for strongly typed collections.
Comparer: Compares two objects for equality, where string comparison is case-sensitive.
DictionaryBase: Provides an abstract base class for strongly typed collections of key/value pairs
Hashtable: Represents a collection of key/value pairs organized according to the hash code of the key.
Queue: Represents a first-in-first-out collection of objects
ReadOnlyCollectionBase: Provides an abstract base class for strongly typed non-generic read-only collections.
SortedList: Represents a collection of key/value pairs that are sorted by key and accessible by key and index.
Stack: Represents a simple last-in-first-out non-generic collection of objects.
Interface:
ICollection: Defines the size, enumeration and synchronization methods of all non-generic collections.
IComparer: Exposes a method for comparing two objects.
IDictionary: Represents a non-universal collection of key/value pairs.
IDictionaryEnumerator: Enumerate the elements of a non-generic dictionary.
IEnumerable: Public enumerator that supports simple iteration over non-generic collections.
IEnumerator: Supports simple iteration of non-generic collections.
IEqualityComparer: Defines methods to support equality comparison of objects.
IList: Represents a non-generic collection of objects that can be accessed individually by index.
Mainly look at the ICollection interface and IEnumerable interface.
ICollection:
This interface defines two main specifications for its implementation class:
(1) The number of collection elements, that is, the Count attribute;
(2) Iteration (GetEnumerator method).
The GetEnumertor method is inherited from ICollection's parent interface IEumerable. The ICollection interface defines a collection that stores and obtains references to object type objects, so that references to various reference type objects or value type objects can be stored and obtained.
IEnumerable interface:
This interface is the parent interface of ICollection. This interface provides iterable capabilities for the classes it implements. The IEumerable interface has only one GetEnumerator method, which returns an enumerator that iterates through the collection
2. Iteration
Iteration, also called iterator, is the iteration mode in the design pattern. The meaning is: providing a method for sequential access. Aggregates the elements in an object without exposing the object's internal representation. Because the storage methods of collections are different, List is continuous storage, and linked list uses reference storage between objects... Then it is inconvenient when you need to traverse collections, and you need a method that can traverse all different collections. This has iterators.
The iterator treats the combined class as an infinite-capacity container, and the storage rules are linear. That is, every element except the first and last one has a direct predecessor and direct successor, and the container has a flag that can point to any storage unit in the container. There are two ways: one-way iteration and two-way iteration.
(1) One-way iteration
One-way iteration refers to forward iteration only. The unit mark of the set can only move backward one by one starting from an element of the set. Therefore, iteration defines three operations:
a. Current item
b. Go to the next item and determine whether it is the end
c. Return to the initial item

(2), Bidirectional iteration mode
For bidirectional iteration mode, The unit mark of the set can move backward one by one starting from an item in the set, or it can move forward one by one starting from an item in the set. Therefore, there are four operations:
a, current item
b, forward to Next item and judge whether it is the end
c, go back to the previous item and judge whether it is the beginning of the set
d, return to the initial position

.net framework defines a one-way iteration specification using the IEumerable interface. The ICollection interface inherits the IEumerable interface. The GetEnumerator method defined by this interface can obtain an iterative object of the current collection class object, that is, an object that implements the IEumerable interface.
Any class that implements the IEnumerable interface can be iteratively traversed using a foreach loop.
The IEnumerator interface defines an iterator that can traverse object type object references, and the IEnumerable interface defines a method for obtaining such an iterator object.
3. Generic collection
ICollection interface
ICollection interface defines a generic collection interface. The so-called generic collection uses the generic features provided by the .net Framework to make the collection A collection of data that is restricted to storing only one specific type of object reference or value type. Generic collections enhance the efficiency and security of collection access.
Since the storage type has been determined, ICollection provides more methods than the ICollection interface, including adding to the collection, deleting from the collection, and determining whether an object reference (or object value) exists in the collection.
IEnumerable interface
The ICollection interface implements the IEnumerable interface, which is mainly used to return an iterative sub-object of a certain type that implements the IEnumerator interface.

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