[转帖]Hashtable简易数据库程序

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import java.io.*;  
, o* _; U2 ~( a( m8 ?* M" f4 Z1 Kimport java.util.*;  
+ V) J# ^- F. V4 [7 J9 uclass str14  
; `# p& a) p6 I( m8 F+ ^( H{  
InputStreamReader stdin=new InputStreamReader(System.in);  
BufferedReader bufin=new BufferedReader(stdin);  

public static void main(String args[]) throws IOException  
6 C' b2 P/ _# Z{  
new str14();//run the application  
}  

public str14() throws IOException//constructor  
{  
Hashtable htable=new Hashtable(20,0.75F);  
dataBase(htable);  
}  
. {4 y0 o( C( {2 Y* Q
7 L, q# o! g2 K! [& mpublic str14(Hashtable htable) throws IOException //override the constructor  
{  
7 i9 w. v& c* E: n- X4 fdataBase(htable);  
}  
* \+ ?# G" [/ {$ u- N
public void dataBase(Hashtable htable) throws IOException  
{  
# E( L9 o4 z+ E2 K9 @int count=htable.size();//get the ammount of the data in htable  
4 S$ B: b: R# Z) Y# H# rint value,id,num;  
- S! s! c! e3 P" K( `String key,enter,data;  
3 z/ u0 _1 f  f+ ^6 \Enumeration keys=htable.keys();//get all the key in htable  
9 C1 H% F8 z* C7 y  VEnumeration elements=htable.elements();//get all the elements in htable  
. N) l+ b+ F' `System.out.println("
- M- h* h0 S0 I2 x/ HHashtable 简易数据库程序
");  
System.out.println("(1)输入数据");  
- S0 l+ n8 s6 Y+ P9 aSystem.out.println("(2)请除所有数据");  
  y; `5 G7 M8 y9 B* J, n+ @+ z; cSystem.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:  
/ d2 o+ F( W- j; \7 YSystem.out.print("
6 `6 L3 G( @: o4 p请输入一笔数据:");//need data input  
data=bufin.readLine();  
count++;  
1 V6 Z. A) P& I: Okey=String.valueOf(count);  
, ]! R/ ~' I+ B  C8 w; Uhtable.put(key,data);//store it to the htable  
: G- t6 f1 o' k% Z: G# u: X7 O, v  {System.out.print("
输入完成，按任意键继续...");  
enter=bufin.readLine();  
- U1 O6 H- T3 H- k$ g, qnew str14(htable);//reenter  
' j/ R0 d) y; i! F& Qbreak;  
case 2://clear all data from the htable  
htable.clear();  
& c; m# l0 g% O7 k3 G, \System.out.print("
- i" x- ~) {- C; s# P" ^; G' G5 |/ X已删除了所有数据... 按任意键继续...");  
3 {, \. l2 ~2 E" f7 N! C6 menter=bufin.readLine();  
, `2 @+ Z, Z& I* V' wnew str14(htable);//reenter  
break;  
case 3:  
System.out.print("
0 W6 {+ e8 f6 i请输入要显示的数据编号:");  
4 ^! s( v* x# \/ J% L& m9 K* Jid=getid(count);//call getid()  
key=String.valueOf(id);  
Object select=htable.get(key);//fetch the data from the htable  
data=select.toString();  
1 m, a" K  m: [. b0 ISystem.out.print("
  I! \8 V+ _7 J' ]* [  c4 I编号"+" "+"内容");  
System.out.println("
  x" Z- P. j; O$ |) K7 q6 B$ b "+key+" "+data);//display the data  
System.out.print("
按任意键继续...");  
( |$ R% a$ u2 D! w; H( nenter=bufin.readLine();  
9 l% j9 Y" o: J9 J/ k" N8 b) jnew str14(htable);//reenter  
break;  
0 A8 e" f3 [1 v3 h; Xcase 4:  
+ u9 f  m4 W& l# `System.out.print("请输入要删除的数据编号:");  
id=getid(count);  
key=String.valueOf(id);  
3 n! d* _) Y! X5 L, E/ xhtable.remove(key);//remove data  
count--;  
' f* @  [8 }7 `1 F. C) B, knum=count;  
System.out.print("已删除了所选择的数据...按任意见继续...");  
, d- U7 \  a7 N  t8 N, WHashtable htable1=new Hashtable(20,0.75F);//create new htable named htable1  
elements=htable.elements();//fetch all the data from htable  
while(elements.hasMoreElements())  
{  
0 W6 P2 W! Z) Lkey=String.valueOf(num);//a new value  
data=(String)elements.nextElement();//fetch content of the data  
4 [3 T5 c) [) R( [0 A1 }8 M7 H3 Bhtable1.put(key,data);//store it to htable1  
num--;  
$ A( C  \5 O2 R! s+ s}  
6 g, r! R9 F8 chtable.clear();  
# j' N% w* h$ L. penter=bufin.readLine();  
new str14(htable1);  
break;  
case 5:  
String[] sortkey=new String[count];//create a new sort array  
String[] sortdata=new String[count];  
' x- [- ]% |5 R# z9 U- Mnum=count;  
: E% W  ?1 k7 [, [+ @elements=htable.elements();  
keys=htable.keys();  
while(elements.hasMoreElements())  
3 }2 y( C6 n) j% Y0 H. b5 \2 S6 _{  
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--;  
, P1 \% ~1 M6 o/ |' D8 q+ A}  
3 m* V( `) g" Z# W# l- S; F" ASystem.out.println("
# c; Y0 _, I" g5 G$ D' G编号"+" "+"内容");  
for(int i=0;i<count;i++)//display all content after sorting  
+ @( _+ a( M* d! D3 M. `% RSystem.out.println(" "+sortkey+" "+sortdata);  
System.out.print("
! X8 g+ ~* ^# q目前共有"+count+"笔数据");  
System.out.print("

按任意键继续...");  
* ^4 T8 c% z* I; [% renter=bufin.readLine();  
new str14(htable);  
break;  
default:  
}  
}  
. k! A3 Q0 ~7 R! c  d1 ~, h
public int select() throws IOException//method of getting a function selector  
; E6 P" _  Q6 [6 I5 E: d6 {{  
String input;  
int value=0;  
3 c5 W& _, G4 `' D! u( vinput=bufin.readLine();//read a input from keyboard  
% V6 j6 {8 f; p5 C8 htry  
5 h# D% u. E; I, K5 X1 b5 H{  
1 Z6 c4 @6 b5 L: b& @; H  K- Tvalue=Integer.parseInt(input);//convert a string to a int value  
}catch(NumberFormatException e)//can’t vonverted  
8 o, g' V9 {0 J0 L{  
/ S1 D3 _# {8 y/ e/ w' |$ ]System.out.print("请输入选项1~6:");  
value=select();  
}  
if(value>6||value<1)//if exceed then print a message and reenter  
{  
System.out.print("请输入选项1~6:");  
value=select();  
}  
return value;//return a value  
}  

public int getid(int count)throws IOException//a method of return the number of data  
( ]& K# C5 g/ X1 I) n{  
5 J  J. E& G: PString input;  
int value=0;  
: a& _- C3 S4 q' ?# f  N3 finput=bufin.readLine();//read a user input string from keyboard  
2 T, K0 E& }' b# o4 ~8 Q7 Ztry  
{  
value=Integer.parseInt(input);//convert the string to a int  
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  
; L4 D! Z. X$ S; n" K{  
: C5 b1 X/ T3 d; e0 Y' d4 A* QSystem.out.print("请输入数据编号:");  
value=getid(count);  
9 T0 E4 n* T0 @8 g# S}  
) u, N( \" c: ]1 w4 Zif(value>count)//the input value is out of bound  
: U; v5 U7 H2 N: o- h" `& ?{  
System.out.print("无此编号的数据,请重新输入:");  
getid(count);  
0 E) p0 M7 U$ X4 b/ s}  
7 `' s8 \# e+ c  _4 |% Creturn value;//return a value  
}  
1 A+ a; D/ `* S, F9 k}