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[转帖]Hashtable简易数据库程序

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电梯直达

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发表于 2005-3-31 01:45 |只看该作者 |倒序浏览

|招呼Ta 关注Ta

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);
6 R8 j6 M! C# u) K6 b: w% K% {System.out.print("! V' E- H& b  C9 [6 f# O% m
目前共有"+count+"笔数据");
: n$ M; B/ u! |) @! }" KSystem.out.print("
" E7 e$ L  S2 j5 E/ k6 W  T2 [$ @3 l9 ^) Q
按任意键继续...");
& C7 Q; ?4 _  U& G5 k9 N3 N4 J# ienter=bufin.readLine();
1 A) ]0 _+ {3 k$ Y8 e- [new str14(htable);
7 u8 s* k% @+ Y' p# P$ d: Zbreak;  ) n6 C/ R( ?5 A) r. ], z: E, u
default:
& ]3 C! }' @) ~( v& R: m9 ^}
4 M7 k5 J0 I/ I3 e}
8 [  [  V0 A* \
. u3 B, w2 h; R. B- z) v$ h4 epublic int select() throws IOException//method of getting a function selector    U/ C/ ?$ s* {. j
{  " @* h6 r- _( Z# D7 [9 |: y
String input;  4 w) s) j; k$ H6 |3 y( l! L
int value=0;
3 p* i, B' B* K4 cinput=bufin.readLine();//read a input from keyboard
& w0 g  ]4 K' k  v7 rtry  0 W) C; @# E# g
{
. ~+ @  d/ w5 xvalue=Integer.parseInt(input);//convert a string to a int value
3 R+ c$ w' ~! U7 L4 M}catch(NumberFormatException e)//can’t vonverted  . |2 B2 s* |! Y0 F" X9 `. m/ r
{  % w0 k4 S! c' {3 m
System.out.print("请输入选项1~6:");
' w3 N- o6 z$ F" y$ j) O7 svalue=select();
3 a6 x4 o* f7 u  F}
# y3 a) T7 S- r; M! o) C' d% H6 Jif(value>6||value<1)//if exceed then print a message and reenter
9 b9 Q4 D# o: [$ G7 O; ]{  # I' Q. p6 `/ P8 R6 s
System.out.print("请输入选项1~6:");
2 x& K9 V* k0 p* I  ?value=select();
: m( {/ d9 [" V# d8 J7 k! H  [}  * B! m) \+ r/ J  t0 A0 ^/ j
return value;//return a value  0 z2 k# ~% v" A6 C
}  2 _" x! {7 Q0 a  J! D

) P! Q4 Q% w5 ]public int getid(int count)throws IOException//a method of return the number of data  3 i: n. d% _3 z& E
{
& ?$ Z. }3 m2 P" `. F9 Y8 B% r0 pString input;
5 u6 N$ I' s* P: [+ c) Q0 eint value=0;  - T' t- L% @) I
input=bufin.readLine();//read a user input string from keyboard
* D% U% I* `& b4 \$ S. e0 Qtry
+ t4 {2 X6 I) g{
# y+ c' l2 J% P: Tvalue=Integer.parseInt(input);//convert the string to a int
" o: D, e* U9 f7 j}catch(NumberFormatException e)//if can’t convert to a integer then reenter  8 U3 [- Q, U9 @9 U: B
{  : ^; O. [$ J6 H9 A8 t
System.out.print("请输入数据编号:");
! E. O% q: D$ I' U/ O; q1 P8 L* Pvalue=getid(count);  3 T0 q( E+ b) u" }9 @0 M
}
  q2 S( M/ w- t( a' H' y5 n1 kif(value>count)//the input value is out of bound
; S8 t* S( W6 _5 I: c/ ~- l{
4 \8 V: Z! B( O, P$ w" s! MSystem.out.print("无此编号的数据,请重新输入:");    i/ l0 S; M. l, C* v& j3 R5 O& i
getid(count);  ; c  P7 a6 r  E5 y9 A! u# s
}
3 }! S' G& d" r- ureturn value;//return a value
$ c' i& X; u" ~/ l0 a# @}
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