hashtable example from MSDN

谁践踏了优雅 2022-08-25 12:47 139阅读 0赞

using System;  
using System.Collections;  
  
class Example  
\{  
    public static void Main()  
    \{  
        // Create a new hash table.  
        //  
        Hashtable openWith = new Hashtable();  
  
        // Add some elements to the hash table. There are no   
        // duplicate keys, but some of the values are duplicates.  
        openWith.Add("txt", "notepad.exe");  
        openWith.Add("bmp", "paint.exe");  
        openWith.Add("dib", "paint.exe");  
        openWith.Add("rtf", "wordpad.exe");  
  
        // The Add method throws an exception if the new key is   
        // already in the hash table.  
        try  
        \{  
            openWith.Add("txt", "winword.exe");  
        \}  
        catch  
        \{  
            Console.WriteLine("An element with Key = /"txt/" already exists.");  
        \}  
  
        // The Item property is the default property, so you   
        // can omit its name when accessing elements.   
        Console.WriteLine("For key = /"rtf/", value = \{0\}.", openWith\["rtf"\]);  
  
        // The default Item property can be used to change the value  
        // associated with a key.  
        openWith\["rtf"\] = "winword.exe";  
        Console.WriteLine("For key = /"rtf/", value = \{0\}.", openWith\["rtf"\]);  
  
        // If a key does not exist, setting the default Item property  
        // for that key adds a new key/value pair.  
        openWith\["doc"\] = "winword.exe";  
  
        // ContainsKey can be used to test keys before inserting   
        // them.  
        if (!openWith.ContainsKey("ht"))  
        \{  
            openWith.Add("ht", "hypertrm.exe");  
            Console.WriteLine("Value added for key = /"ht/": \{0\}", openWith\["ht"\]);  
        \}  
  
        // When you use foreach to enumerate hash table elements,  
        // the elements are retrieved as KeyValuePair objects.  
        Console.WriteLine();  
        foreach( DictionaryEntry de in openWith )  
        \{  
            Console.WriteLine("Key = \{0\}, Value = \{1\}", de.Key, de.Value);  
        \}  
  
        // To get the values alone, use the Values property.  
        ICollection valueColl = openWith.Values;  
  
        // The elements of the ValueCollection are strongly typed  
        // with the type that was specified for hash table values.  
        Console.WriteLine();  
        foreach( string s in valueColl )  
        \{  
            Console.WriteLine("Value = \{0\}", s);  
        \}  
  
        // To get the keys alone, use the Keys property.  
        ICollection keyColl = openWith.Keys;  
  
        // The elements of the KeyCollection are strongly typed  
        // with the type that was specified for hash table keys.  
        Console.WriteLine();  
        foreach( string s in keyColl )  
        \{  
            Console.WriteLine("Key = \{0\}", s);  
        \}  
  
        // Use the Remove method to remove a key/value pair.  
        Console.WriteLine("/nRemove(/"doc/")");  
        openWith.Remove("doc");  
  
        if (!openWith.ContainsKey("doc"))  
        \{  
            Console.WriteLine("Key /"doc/" is not found.");  
        \}  
    \}  
\}  
  
/\* This code example produces the following output:  
  
An element with Key = "txt" already exists.  
For key = "rtf", value = wordpad.exe.  
For key = "rtf", value = winword.exe.  
Value added for key = "ht": hypertrm.exe  
  
Key = dib, Value = paint.exe  
Key = txt, Value = notepad.exe  
Key = ht, Value = hypertrm.exe  
Key = bmp, Value = paint.exe  
Key = rtf, Value = winword.exe  
Key = doc, Value = winword.exe  
  
Value = paint.exe  
Value = notepad.exe  
Value = hypertrm.exe  
Value = paint.exe  
Value = winword.exe  
Value = winword.exe  
  
Key = dib  
Key = txt  
Key = ht  
Key = bmp  
Key = rtf  
Key = doc  
  
Remove("doc")  
Key "doc" is not found.  
\*/

注意当给的key 不在hashtable 中时，可以

openWith\["doc"\] = "winword.exe";  
来添加新key/element对。

// When you use foreach to enumerate hash table elements,  
        // the elements are retrieved as KeyValuePair objects.  
        Console.WriteLine();  
        foreach( DictionaryEntry de in openWith )  
        \{  
            Console.WriteLine("Key = \{0\}, Value = \{1\}", de.Key, de.Value);  
        \}  
  
        // To get the values alone, use the Values property.  
        ICollection valueColl = openWith.Values;  
  
        // The elements of the ValueCollection are strongly typed  
        // with the type that was specified for hash table values.  
        Console.WriteLine();  
        foreach( string s in valueColl )  
        \{  
            Console.WriteLine("Value = \{0\}", s);  
        \}  
  
        // To get the keys alone, use the Keys property.  
        ICollection keyColl = openWith.Keys;  
  
        // The elements of the KeyCollection are strongly typed  
        // with the type that was specified for hash table keys.  
        Console.WriteLine();  
        foreach( string s in keyColl )  
        \{  
            Console.WriteLine("Key = \{0\}", s);  
        \}