Delphi 6 中使用 Hashtable

在 Delphi 6 中使用 Hashtable 2006-03-14 21:10:00

标签：delphi hashtable

Java 中的 Hashtable 类小巧好用，尤其是因为采用了哈希算法，查找的速度奇快。后来因

工作需要，使用 Delphi 实施一些项目，特别不习惯没有哈希表的日子。于是决定自己动手做

一个。

不必白手起家，Delphi 中有一个 THashedStringList 类，它位于 IniFiles 单元中。它里面

有一个不错的哈希算法，解决冲突的机制是“链地址”。把这个类改装改装，就成了自己的

了。新鲜热辣，火爆出炉。下面就来看看新的 Hashtable 长得何许模样。

Hashtable.pas

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unit Hashtable;

interface

uses SysUtils, Classes;

type

{ THashTable }

PPHashItem = ^PHashItem;

PHashItem = ^THashItem;

THashItem = record

Next: PHashItem;

Key: string;

Value: String;

end;

THashTable = class

private

Buckets: array of PHashItem;

protected

function Find(const Key: string): PPHashItem;

function HashOf(const Key: string): Cardinal; virtual;

public

constructor Create(Size: Integer = 256);

destructor Destroy; override;

procedure Put(const Key: string; Value: String);

procedure Clear;

procedure Remove(const Key: string);

function Modify(const Key: string; Value: String): Boolean;

function Get(const Key: string): String;

end;

implementation

{ THashTable }

procedure THashTable.Put(const Key: string; Value: String);

var

Hash: Integer;

Bucket: PHashItem;

begin

Hash := HashOf(Key) mod Cardinal(Length(Buckets));

New(Bucket);

Bucket^.Key := Key;

Bucket^.Value := Value;

Bucket^.Next := Buckets[Hash];

Buckets[Hash] := Bucket;

end;

procedure THashTable.Clear;

var

I: Integer;

P, N: PHashItem;

begin

for I := 0 to Length(Buckets) - 1 do

begin

P := Buckets[I];

while P <> nil do

begin

N := P^.Next;

Dispose(P);

P := N;

end;

Buckets[I] := nil;

end;

end;

constructor THashTable.Create(Size: Integer);

begin

inherited Create;

SetLength(Buckets, Size);

end;

destructor THashTable.Destroy;

begin

Clear;

inherited;

end;

function THashTable.Find(const Key: string): PPHashItem;

var

Hash: Integer;

begin

Hash := HashOf(Key) mod Cardinal(Length(Buckets));

Result := @Buckets[Hash];

while Result^ <> nil do

begin

if Result^.Key = Key then

Exit

else

Result := @Result^.Next;

end;

end;

function THashTable.HashOf(const Key: string): Cardinal;

var

I: Integer;

begin

Result := 0;

for I := 1 to Length(Key) do

Result := ((Result shl 2) or (Result shr (SizeOf(Result) * 8 - 2))) xor

Ord(Key[I]);

end;

function THashTable.Modify(const Key: string; Value: String): Boolean;

var

P: PHashItem;

begin

P := Find(Key)^;

if P <> nil then

begin

Result := True;

P^.Value := Value;

end

else

Result := False;

end;

procedure THashTable.Remove(const Key: string);

var

P: PHashItem;

Prev: PPHashItem;

begin

Prev := Find(Key);

P := Prev^;

if P <> nil then

begin

Prev^ := P^.Next;

Dispose(P);

end;

end;

function THashTable.Get(const Key: string): String;

var

P: PHashItem;

begin

P := Find(Key)^;

if P <> nil then

Result := P^.Value else

Result := '';

end;

end.

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使用起来就简单了：

HashTable := THashTable.Create(); //创建

HashTable.Put(Key, Value); //赋值

Value=HashTable.Get(Key); //取值

HashTable.Destroy; //撤消

本程序在Delphi 6.0下通过。(其它版本应该也可以，不过没做测试)

附件：http://down.51cto.com/data/2358949