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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);  5 C  ^* ~" u2 ~
System.out.print("
0 M! M' M. j* x6 _  u目前共有"+count+"笔数据");
" C7 e! V' a, B' uSystem.out.print("7 @$ r7 x7 V  [6 P3 |2 c2 o

0 u' }3 E6 N+ a2 F9 L. }按任意键继续...");  % G& b% p% h: l" X- P
enter=bufin.readLine();  % c2 l- p* D3 d
new str14(htable);  5 t6 z; F3 W* v
break;  7 k/ X" M$ \0 D$ C* I+ J9 W5 T
default:
) A# y$ g$ @! P: t  [8 u( j: y. M}  8 z# `5 o! v: H& J# r2 K
}    n2 l1 t) e' M

) T8 M( c- D9 s- L$ opublic int select() throws IOException//method of getting a function selector  - h9 J# d, a6 k1 ]" i# Y
{  7 G0 p4 `" l: ~0 r+ }6 H
String input;
3 ~$ z2 h: {# k% ^int value=0;
3 _5 y/ ~9 W4 C* h  linput=bufin.readLine();//read a input from keyboard
9 H- ~: I, H0 A! Vtry  ! `3 _% C/ [+ _8 ~+ w+ e- B! y+ Y; l! R
{
/ q' x+ G0 V& @# nvalue=Integer.parseInt(input);//convert a string to a int value
% m" P1 j9 m1 j- }5 [}catch(NumberFormatException e)//can’t vonverted
. G' [8 {$ O, R5 C  {& s# _6 F{
& I! {+ |$ D2 W% K+ a* k3 XSystem.out.print("请输入选项1~6:");  1 S  R1 E- W/ P2 n, q" |! \; I
value=select();  , F4 M7 \5 Q2 d, X
}
$ N/ q4 @  d9 @8 k& |if(value>6||value<1)//if exceed then print a message and reenter  ( h7 v0 T, l# D: d, P
{  ' a6 ^6 ^; Z0 K" R; y
System.out.print("请输入选项1~6:");  : W! ]0 o: p" f8 {) F' |
value=select();
: Q2 i; C" H. J2 a" F0 m6 T; g: c9 R}
, c- z: P& i/ x" L" d7 yreturn value;//return a value
, |9 m/ S) W* B1 w" R4 }% {}  + D: m( \  h/ D- D" E0 P

% g6 `2 I  f. g) o7 e& |' r( mpublic int getid(int count)throws IOException//a method of return the number of data  * B+ \" C1 d8 p9 C4 ^$ I8 t
{
9 r2 g/ J% p& K/ ~' m/ zString input;
5 A, n- s3 f! j6 c% r5 u6 x0 P1 Zint value=0;
+ q( u# [) H1 \2 r  finput=bufin.readLine();//read a user input string from keyboard  2 k( r) @/ B, Q; i$ w, b
try  - Q: T! Y: o: q9 b
{
. R2 n: Q! l  }value=Integer.parseInt(input);//convert the string to a int  8 d% ^6 E" v! g3 I& G. M) n; s
}catch(NumberFormatException e)//if can’t convert to a integer then reenter
% j  T: `/ u( \2 r{  " @& l8 w  L6 s+ K
System.out.print("请输入数据编号:");
3 r  r- E  R4 |value=getid(count);    d+ c6 r* |; _0 h
}
$ c7 q7 C" \- ]- |8 c& J( ]6 o; Q2 tif(value>count)//the input value is out of bound
3 I! [0 a2 R; p" G+ T( p2 X$ T{
+ {( @7 w: l6 h2 g9 RSystem.out.print("无此编号的数据,请重新输入:");
) l3 E% S+ X) c! X3 F  ~getid(count);
/ Y0 x& o! u# C+ a6 i}  , u' D4 f8 I  z, Q! H- b% [
return value;//return a value
; S$ a% G" |. X/ G7 f}
' y8 F% q% z$ c}