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标题: [转帖]Hashtable简易数据库程序 [打印本页]

作者: god 时间: 2005-3-31 01:45
标题: [转帖]Hashtable简易数据库程序
import java.io.*;
import java.util.*;
class str14
{
InputStreamReader stdin=new InputStreamReader(System.in);
BufferedReader bufin=new BufferedReader(stdin);

public static void main(String args[]) throws IOException
{
new str14();//run the application
}

public str14() throws IOException//constructor
{
Hashtable htable=new Hashtable(20,0.75F);
dataBase(htable);
}

public str14(Hashtable htable) throws IOException //override the constructor
{
dataBase(htable);
}

public void dataBase(Hashtable htable) throws IOException
{
int count=htable.size();//get the ammount of the data in htable
int value,id,num;
String key,enter,data;
Enumeration keys=htable.keys();//get all the key in htable
Enumeration elements=htable.elements();//get all the elements in htable
System.out.println("
Hashtable 简易数据库程序
");
System.out.println("(1)输入数据");
System.out.println("(2)请除所有数据");
System.out.println("(3)显示单笔数据");
System.out.println("(4)删除单笔数据");
System.out.println("(5)显示所有数据");
System.out.println("(6)结束程序");
System.out.print("请输入您的选择:");
value=select();//call select(),return the function number
switch(value)//the function
{
case 1:
System.out.print("
请输入一笔数据:");//need data input
data=bufin.readLine();
count++;
key=String.valueOf(count);
htable.put(key,data);//store it to the htable
System.out.print("
输入完成，按任意键继续...");
enter=bufin.readLine();
new str14(htable);//reenter
break;
case 2://clear all data from the htable
htable.clear();
System.out.print("
已删除了所有数据... 按任意键继续...");
enter=bufin.readLine();
new str14(htable);//reenter
break;
case 3:
System.out.print("
请输入要显示的数据编号:");
id=getid(count);//call getid()
key=String.valueOf(id);
Object select=htable.get(key);//fetch the data from the htable
data=select.toString();
System.out.print("
编号"+" "+"内容");
System.out.println("
"+key+" "+data);//display the data
System.out.print("
按任意键继续...");
enter=bufin.readLine();
new str14(htable);//reenter
break;
case 4:
System.out.print("请输入要删除的数据编号:");
id=getid(count);
key=String.valueOf(id);
htable.remove(key);//remove data
count--;
num=count;
System.out.print("已删除了所选择的数据...按任意见继续...");
Hashtable htable1=new Hashtable(20,0.75F);//create new htable named htable1
elements=htable.elements();//fetch all the data from htable
while(elements.hasMoreElements())
{
key=String.valueOf(num);//a new value
data=(String)elements.nextElement();//fetch content of the data
htable1.put(key,data);//store it to htable1
num--;
}
htable.clear();
enter=bufin.readLine();
new str14(htable1);
break;
case 5:
String[] sortkey=new String[count];//create a new sort array
String[] sortdata=new String[count];
num=count;
elements=htable.elements();
keys=htable.keys();
while(elements.hasMoreElements())
{
key=(String)keys.nextElement();//fetch value of key
data=(String)elements.nextElement();//fetch value of data
sortkey[num-1]=key;//store the value of key to sortkey array
sortdata[num-1]=data;//store the value of data to sortdata array
num--;
}
System.out.println("
编号"+" "+"内容");
for(int i=0;i<count;i++)//display all content after sorting
System.out.println(" "+sortkey+" "+sortdata);
7 k( M! w/ ?, a; v7 z- cSystem.out.print("
; n- n$ F* V4 h" {6 t( U目前共有"+count+"笔数据");  2 J! ]- }; c, V8 J
System.out.print("
' G' h/ [8 i' w% H
3 I8 K8 w+ ]" A* p: f) Z; B按任意键继续...");  % i, g" x9 J" m) u. _9 R
enter=bufin.readLine();
: I3 L7 i, [& k0 V9 rnew str14(htable);  # n5 `4 `. _& @+ E/ h& w+ g7 n
break;
- f" }* G. Q+ h- B1 m% K3 ndefault:
) Z9 L  [% `' b' k  S}
6 h2 y0 i2 ]! V  Y}
( _( i( B! a. J! |1 l. }+ W4 }: K9 ^  z. Q/ d
public int select() throws IOException//method of getting a function selector  4 T) N: \1 M% ~# V4 o% D
{
- Y# e% k4 n; V) ?2 g% WString input;  ; b# a" ^9 `: C0 S
int value=0;
+ s% e; V" S% V' ginput=bufin.readLine();//read a input from keyboard
5 K: B/ ]: |3 x) m1 Ftry
) U! l- z  b: g& w; h  m! |+ ]{  . H% ?, [2 b+ H
value=Integer.parseInt(input);//convert a string to a int value
+ I: H9 ^% z6 f7 [4 ^/ T}catch(NumberFormatException e)//can’t vonverted  , @5 b9 g, {- q1 J
{  * K  g6 P) n2 j% O: ]
System.out.print("请输入选项1~6:");  ; X! W6 p% q6 `+ C# q! G
value=select();
9 h& Z% x0 J& Q' X}
$ S# D6 o. q- @0 O' Kif(value>6||value<1)//if exceed then print a message and reenter  # g9 N' j2 a! d2 |0 `/ h
{  ) R5 w5 l; d! }" Q# c) C
System.out.print("请输入选项1~6:");
/ [; G  N' R3 N( vvalue=select();
& X' x* S7 \2 j' c}  . D2 q' p% [6 `  r% S
return value;//return a value
( i( a. E1 W' ~- O}  * O* g" f# u( S- y

* O& n" d8 a4 z1 N4 Zpublic int getid(int count)throws IOException//a method of return the number of data  ; f3 z% g5 |# M
{  2 H6 p' F+ h& n9 r
String input;  * g: J# C! U" }5 O0 o; [
int value=0;
& j9 G1 V/ @* }input=bufin.readLine();//read a user input string from keyboard  - Z! X: @0 z3 N- {0 _
try
! k( V7 _" ~0 O/ `{    u$ d9 s' {0 A/ M
value=Integer.parseInt(input);//convert the string to a int  + |" }& ^: Z3 [! B9 I
}catch(NumberFormatException e)//if can’t convert to a integer then reenter
+ T+ ?* W1 j  J0 v% }5 \+ G9 g8 h{
  Y8 {! m$ {" q1 q9 C. R! I5 o4 TSystem.out.print("请输入数据编号:");
+ e; L$ R: n/ d: bvalue=getid(count);  0 `& R. s3 ?/ A- Z
}
6 A' X+ A) m$ Z; ^2 L+ pif(value>count)//the input value is out of bound  $ v1 S/ v& X3 _" B" d
{
7 \0 G- ?! a7 y; J5 x0 KSystem.out.print("无此编号的数据,请重新输入:");
5 C; G  F; i% v  p% Kgetid(count);  ) A! Y# _, l" U
}
( A: o1 T7 D( o, ?0 ^7 Nreturn value;//return a value  2 }6 G" ]( f1 I/ ~2 R; M
}
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