[转帖]Hashtable简易数据库程序

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import java.io.*;  
import java.util.*;  
class str14  
+ j& _- a, I; C7 }- b{  
InputStreamReader stdin=new InputStreamReader(System.in);  
BufferedReader bufin=new BufferedReader(stdin);  

public static void main(String args[]) throws IOException  
{  
new str14();//run the application  
}  
- U" `! T0 |5 V
( l- z3 ?3 `9 l) u( F; Spublic str14() throws IOException//constructor  
{  
Hashtable htable=new Hashtable(20,0.75F);  
/ _7 }8 D3 e2 o  o% A5 k! a3 idataBase(htable);  
}  

public str14(Hashtable htable) throws IOException //override the constructor  
{  
& r3 [* l5 @# GdataBase(htable);  
}  

+ [/ w# V  a1 w9 n7 rpublic void dataBase(Hashtable htable) throws IOException  
, l" F6 y2 i! R{  
& ^1 J* K& A+ X" t: K8 jint count=htable.size();//get the ammount of the data in htable  
+ Z' \) i5 ~7 Rint value,id,num;  
String key,enter,data;  
Enumeration keys=htable.keys();//get all the key in htable  
/ G$ o; X$ B4 J1 Y+ n- vEnumeration elements=htable.elements();//get all the elements in htable  
/ D% h  _9 Z$ b6 e/ HSystem.out.println("
  c( z) M  h5 |. E7 bHashtable 简易数据库程序
1 t" P) e  \/ P6 N9 r7 \" U5 G");  
4 ?. A/ f! K7 F) F% j1 USystem.out.println("(1)输入数据");  
( F; W! r8 K# s2 ZSystem.out.println("(2)请除所有数据");  
6 T3 x& X' o! PSystem.out.println("(3)显示单笔数据");  
System.out.println("(4)删除单笔数据");  
4 a" Z( c# u- q' ZSystem.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:");  
" n) t  m! [9 Z# x' _8 L- g5 Hvalue=select();//call select(),return the function number  
switch(value)//the function  
' |" J9 q; x) @- a{  
8 b* u/ j: L) H+ r+ Ucase 1:  
, l6 q2 n# R! |- `4 DSystem.out.print("
: C$ j6 A. n* G7 N请输入一笔数据:");//need data input  
data=bufin.readLine();  
count++;  
key=String.valueOf(count);  
- P1 i5 s- b, v2 {* lhtable.put(key,data);//store it to the htable  
/ h7 b7 C1 R4 U/ s% s2 i/ y5 Y2 y( _& }System.out.print("
输入完成，按任意键继续...");  
, T( S3 _+ X. b$ L  [4 Benter=bufin.readLine();  
6 \" v/ q( }1 c+ u. Tnew str14(htable);//reenter  
break;  
+ W$ i1 W1 r, Hcase 2://clear all data from the htable  
htable.clear();  
System.out.print("
% k0 N3 `- G' ~% U: D6 a/ {已删除了所有数据... 按任意键继续...");  
1 e( D: ?! w- S/ F) zenter=bufin.readLine();  
new str14(htable);//reenter  
8 n2 {4 }; l. k- h: @8 a" Z4 Vbreak;  
/ s. M# K3 c! \0 m( S' ]case 3:  
System.out.print("
% A% I+ [0 O" c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  
; x* ~$ `3 w. }+ fdata=select.toString();  
System.out.print("
编号"+" "+"内容");  
System.out.println("
"+key+" "+data);//display the data  
; }! K8 o' Z: KSystem.out.print("
按任意键继续...");  
enter=bufin.readLine();  
new str14(htable);//reenter  
break;  
case 4:  
+ x0 ~3 L) E2 c& k5 K: W" q2 hSystem.out.print("请输入要删除的数据编号:");  
id=getid(count);  
# o  ?& u0 a( q3 akey=String.valueOf(id);  
htable.remove(key);//remove data  
  }+ Z; z* X. T2 q' wcount--;  
2 d" N* q4 q) u0 b3 X( S9 Vnum=count;  
System.out.print("已删除了所选择的数据...按任意见继续...");  
" w7 s& e$ `5 S) E4 Y) Q* ^0 YHashtable htable1=new Hashtable(20,0.75F);//create new htable named htable1  
* A0 O! Z, F" \& k7 w  nelements=htable.elements();//fetch all the data from htable  
while(elements.hasMoreElements())  
1 x0 G4 ^: I) ]* }0 a8 g{  
key=String.valueOf(num);//a new value  
data=(String)elements.nextElement();//fetch content of the data  
. D3 R7 @  W; R; h/ b; ]% X) q2 Ohtable1.put(key,data);//store it to htable1  
num--;  
5 p. ]' Y7 t3 y( C: s1 t8 ]$ C}  
htable.clear();  
enter=bufin.readLine();  
( F2 J$ M# p5 ~- J7 Qnew str14(htable1);  
0 D6 k' K* \  P: ^break;  
* p; z6 v- V$ e% U( ccase 5:  
& p2 p, v' w! [String[] sortkey=new String[count];//create a new sort array  
String[] sortdata=new String[count];  
num=count;  
elements=htable.elements();  
5 F6 h! g' i+ n: e) @  q, Zkeys=htable.keys();  
$ ~; \# \0 K! w9 v8 `1 xwhile(elements.hasMoreElements())  
* C# ]" C. z, C, i' D# ]{  
key=(String)keys.nextElement();//fetch value of key  
3 V2 Z/ w! o' U8 Edata=(String)elements.nextElement();//fetch value of data  
sortkey[num-1]=key;//store the value of key to sortkey array  
/ F$ J. n  w6 J  Z/ ~6 \sortdata[num-1]=data;//store the value of data to sortdata array  
num--;  
}  
System.out.println("
3 H4 q* u6 v* |5 w7 T6 W编号"+" "+"内容");  
for(int i=0;i<count;i++)//display all content after sorting  
System.out.println(" "+sortkey+" "+sortdata);  
System.out.print("
目前共有"+count+"笔数据");  
System.out.print("
. T" y, x0 Y6 \& K1 R4 c3 p
按任意键继续...");  
enter=bufin.readLine();  
new str14(htable);  
0 y1 [0 b; Q+ q  abreak;  
default:  
6 ~9 Y- ?+ i2 Z4 Q}  
}  

public int select() throws IOException//method of getting a function selector  
" e! w3 F! y; D/ U: z5 \) {4 n{  
String input;  
int value=0;  
* E/ c( o, z1 Z  vinput=bufin.readLine();//read a input from keyboard  
  h, m" g7 W* `: K. itry  
{  
value=Integer.parseInt(input);//convert a string to a int value  
}catch(NumberFormatException e)//can’t vonverted  
: b; S, f. y( D  u{  
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:");  
1 Q2 M, ~* m/ evalue=select();  
}  
' D& {' G5 T* v1 u, b3 Y5 O: U* \( k# _return value;//return a value  
}  
$ _. C# s4 S# T4 i' @/ J
public int getid(int count)throws IOException//a method of return the number of data  
{  
String input;  
int value=0;  
7 t- [& b# f) H* Y7 Z6 d: G4 ninput=bufin.readLine();//read a user input string from keyboard  
try  
{  
7 t: E4 A& x5 x3 r7 b! dvalue=Integer.parseInt(input);//convert the string to a int  
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  
+ N. C6 q& H8 i{  
System.out.print("请输入数据编号:");  
value=getid(count);  
( r% I! A# j5 G: n}  
if(value>count)//the input value is out of bound  
{  
! |+ L" b8 R0 V' _* PSystem.out.print("无此编号的数据,请重新输入:");  
+ A( r0 P7 N; W" ?1 ?: r0 B" vgetid(count);  
}  
8 C9 [, p9 `" c3 Lreturn value;//return a value  
}  
}