Use a set to organize relevant data and a set to organize relevant data
ArrayList is very similar to an array, which is also called an array list. ArrayList can be dynamically maintained.
Tip:
Similar to arrays, the data stored in ArrayList is called an element. The number of elements that can be saved in ArrayList is the size of ArrayList. The default initial capacity is 0. You can access the elements in ArrayList through indexes, index starts from 0
ArrayList belongs to the System. Collections namespace and is a collection type.
Using System. Collection
ArrayList arr = new ArrayList ();
ArrayList common methods and attributes
Attribute Name Description
Count: obtains the number of actually contained elements in the ArrayList.
Return Value Type Method Name Description
Int Add (Object value) adds the Object to the end of ArrayList
Void RemoveAt (int index) removes the element at the specified index in ArrayList.
Void Remove (Object value) removes a specific Object from ArrayList
Void Clear () removes all elements from ArrayList
Add data to ArrayList
1. ArrayList Add elements using the Add Method
Returned value: the value is of the int type and is used to return the index of the element.
Parameter: If the elements added to the ArrayList are of the value type, these elements will be converted to the Object reference type and saved. Therefore, all the elements in the ArrayList are references to objects.
Access a single element in the ArrayList
The method used by ArrayList to obtain an element is the same as that of an array. It is also accessed through an index. The index of the first element in ArrayList is 0.
Traverse elements in ArrayList
Int [] array = new int [] {1, 2, 3, 4, 5 };
For (int I = 0; I <array. length; I ++ ){
Console. WriteLine (array [I]);
}
Delete an element from ArrayList
ArrayList engineers = new ArrayList ();
Engineers. RemoveAt (0 );
Enginneers. Remove (ema );
MessageBox. Show (string. Format ("{0} engineers in all departments", engineers. Count. Tostring ()));
SE leave = (SE) engineers [0];
MessageBos. Show (leave. SayHi ());
The RemoveAt () and Remove () methods can delete only one element.
Hashtable
Common methods and attributes of Hashtable
Attribute Name Description
Count: gets the number of key/value pairs contained in Hashtable.
Keys obtains the set contained in the Hashtable key.
Values obtains the set containing the Hashtable value.
Return Value Type Method Name Description
Void Add (Object key, Object value) adds elements with specified keys and values to Hashtable
Void Remove (Object key) Removes elements with specific keys from Hashtable
Void Clear () removes all elements from Hashtable
Hashtable adds elements through the Add () method
The Add () method of Hashtable has two parameters, one representing the key and the other representing the value not corresponding to the key.
Traverse elements in Hashtable
Foreach (Oject obj in engineers. Keys ){
Console. WirteLine (string) obj );
}
Foreach (Object obj in engineers. Values ){
SE se = (SE) obj;
Console. WriteLine (se. Name );
}
Generic and generic Sets
Generic
Generics introduce the concept of type parameters. By using type parameters (T), you can reduce the risk of forced conversion or packing during running. With generics, You can reuse code to the maximum extent to protect the security of types and improve performance, its most common application is to create a collection class, which can constrain the element types in the Collection class. Typical generic collections are List <T> and Dictionary <>;
List of generic sets <T>
Syntax
List <T> Object Name = new List <T> ();
Difference between List <T> and ArrayList
Similarities and Differences List <T> ArrayList
Different Points impose type constraints on saved elements to add any types.
You do not need to unpack the elements for adding/reading value types. You need to unpack the elements for adding/reading value types.
Similar points: accessing elements in a set through Indexes
The method for adding elements is the same.
The method for deleting elements is the same.
Generic set Dictionary <K, V>
Syntax
Dictionary <K, V> Object Name = new Dictionary <K, V> ();
For example:
Dictionary <string, SE> engineers = new Dictionary <string, SE> ();
Comparison between Dictionary and Hashtable
Similarities and Differences Dictionary <K, V> Hashtable
Different Points impose type constraints on saved elements to add any types.
You do not need to unpack the elements for adding/reading value types. You need to unpack the elements for adding/reading value types.
Same point, get Value through Key
The method for adding elements is the same.
The method for deleting elements is the same.
The Traversal method is the same.
Dictionary can also use the following method:
Foreach (KeyValuePair <string, SE> en in engineers ){
Console. WriteLine (en. Key );
Console. WriteLine (en. Value. Name );
}
Generic Type
Syntax
Public class name <T> {
//........
}