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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);  : M! p" H- T0 L, U$ U
System.out.print("
% S, v2 }4 P% J% ~5 L& Z目前共有"+count+"笔数据");  $ O: Z# d) O% _$ `  ~$ c
System.out.print("
7 {0 f5 L2 [2 o& @  d+ h: o. q* E$ t' D
按任意键继续...");
3 r) h: t* P4 L  H/ S$ c! Y' eenter=bufin.readLine();
: g: u: L$ ?9 u0 qnew str14(htable);
( S. s* l8 g. t3 Y: Y  n& Gbreak;
( [! n% l- G6 Wdefault:  5 I. G- o; j" I, A/ k' T3 ]
}  ' G# C/ k3 o5 D$ w! C' a
}    s( y% x0 Y+ a6 U+ z( a+ X% R

+ z1 q# z" u, S4 ?! F6 q8 C; mpublic int select() throws IOException//method of getting a function selector
6 D: z& ~* S: H+ L% N' p8 L{
, c; j8 ^8 v1 t$ y* `' ZString input;  9 R/ i! y' `6 x
int value=0;
$ L  ]. ?5 E  |& S) @: D4 ginput=bufin.readLine();//read a input from keyboard  " `; Y3 P9 h- w) ^3 `2 K# M
try  9 ?) f# d4 d' O: \2 ]5 J# X
{  . L* C* s# m% O
value=Integer.parseInt(input);//convert a string to a int value  . v% f: }4 I2 S0 ~
}catch(NumberFormatException e)//can’t vonverted
- O0 _: V/ P3 W' ^6 E) A{  ! c- x) J+ \% A3 X0 Z5 O2 n
System.out.print("请输入选项1~6:");  % h, Q. U& m; ]0 p0 G5 c
value=select();
( _- Q0 J6 ]" Q& ?  `9 \}
5 U5 Y2 p1 ^; x/ }if(value>6||value<1)//if exceed then print a message and reenter
. @3 e" W2 g( {# u5 l" ?* F{  5 f) b) O) u& C  k$ U' X1 @# a6 _. \5 m
System.out.print("请输入选项1~6:");
% B% g2 C6 T8 f9 ^" H* {1 Avalue=select();
7 U( r- E, J. j4 ]  I}  + H1 |0 D8 S' [" G
return value;//return a value  & M9 P8 R2 c- H2 v3 N# I1 w
}  0 ?' T/ v" p  T7 i% u% w
; O7 S! x" [5 G6 {6 {! q# D6 L
public int getid(int count)throws IOException//a method of return the number of data
7 |; H. X7 F7 E5 p7 G{  - \( r" L% H) R" s3 G
String input;  - T5 u% n8 R2 s+ A- z1 Q
int value=0;
- m2 }2 X; F* m" I  Sinput=bufin.readLine();//read a user input string from keyboard
- `3 V) d0 n0 l1 Ktry
7 J5 Q3 Z( U! h+ N6 l# {3 ?{  . F4 G* [) Q4 C% [6 i
value=Integer.parseInt(input);//convert the string to a int
1 i" f" c$ z4 B}catch(NumberFormatException e)//if can’t convert to a integer then reenter
) k  B! A' ~9 R5 ~+ T4 V2 g7 H+ R5 L{    V, N' n" R+ \( R' O9 y1 C* [" Y
System.out.print("请输入数据编号:");
9 V8 L- d3 R  E- f3 k% i  e! @- Rvalue=getid(count);  * b) ~, o; [) _1 h9 A; [+ @% `$ k
}  " g5 U) J7 N: g: l+ v+ V
if(value>count)//the input value is out of bound  : @  X1 }, L& n" F
{
% m* M3 I0 i" KSystem.out.print("无此编号的数据,请重新输入:");
" i9 `, Y8 v' Bgetid(count);
! S% b9 [# E  V' [$ W}
7 T' ^# D! w" `) n' w7 Qreturn value;//return a value  6 ~  g5 z) t# r  P
}
& C3 c5 K( G8 j' g6 v}