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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);
: ~4 ^0 S+ ^3 y( V8 }$ a4 A. o, q; aSystem.out.print("
/ B4 z6 r4 P; k/ ~0 n$ f. Q! |" a目前共有"+count+"笔数据");  " C3 }2 i4 C( H- A+ j: h# G6 N% W
System.out.print(": d$ Z4 a  c- ^& Y  l& F6 \9 b2 [

6 O! y. Z3 U! z7 q, |8 f, I按任意键继续...");
8 e* N/ C& T  R! \3 R5 x% kenter=bufin.readLine();  ) c) h/ g/ h/ h$ T; W% X! \
new str14(htable);  % o  |* ]1 m# n  [/ A5 j0 `
break;  6 E# e* S& L4 q1 u$ J, ~% G
default:  / j0 i( K( F9 l) Y6 H3 ^. x
}
8 v" s$ ~0 r' g, |7 M}  2 ]2 T' N9 d! k

4 H. a2 W+ A: C. h7 [! jpublic int select() throws IOException//method of getting a function selector
9 L6 J, K5 X% N% z# O{
& Y% o, u' @  M1 L" m5 _String input;
3 V% `% @" o( n3 Mint value=0;
5 z- C! g1 M+ H! `input=bufin.readLine();//read a input from keyboard  1 _; g- v8 R! P
try
5 C. C: ?- x* P, W+ f$ |* z{
+ ^9 h( F; m) J- Svalue=Integer.parseInt(input);//convert a string to a int value  ! N8 s4 I/ z1 }! D5 ]( A& k
}catch(NumberFormatException e)//can’t vonverted  2 q6 i. ~* E) t  q  d
{
% J# F  O2 i3 F" y' E0 ISystem.out.print("请输入选项1~6:");  ) p! d) [% B- H7 D
value=select();  & J! }- z( j: z, C2 K5 _) d
}
. j+ \" [( Z: t/ H4 D7 W7 Z' Uif(value>6||value<1)//if exceed then print a message and reenter
7 n* o9 }6 U$ m{  ( z: |2 y; @. S  O( t. o: @# l: E
System.out.print("请输入选项1~6:");  2 {6 V2 L- j3 L% r9 D
value=select();
" s1 R; \+ I+ E/ }( ?}  , X, J4 h+ ~- q- F; m, c: W
return value;//return a value  9 U  E# `  b6 G. j9 V
}
; [+ v% U+ u6 T. }! I, Z1 i9 I0 ^0 y* S" n( d
public int getid(int count)throws IOException//a method of return the number of data
( u; j) @; _- ~5 X# n! {{
0 ]- y2 |, ^/ X. xString input;  1 P0 H% G7 \& [1 Y1 Q
int value=0;  % c9 l  O9 @- V: p; u- h
input=bufin.readLine();//read a user input string from keyboard
5 e% C: x, T& R4 p! stry  ; g1 P( e7 d, a5 L% w# k7 |4 g  r
{
( u- H8 A0 U1 @3 K* Hvalue=Integer.parseInt(input);//convert the string to a int
3 l! v& m0 e3 c" j}catch(NumberFormatException e)//if can’t convert to a integer then reenter  ( }- ]+ @# G% D9 o
{
0 q. q8 q5 d6 `. p2 h7 rSystem.out.print("请输入数据编号:");
) w' \5 Z7 ]! J, v7 Tvalue=getid(count);    M6 i5 z+ U% }$ w4 Y! K
}
8 v! N# Q+ }- J9 iif(value>count)//the input value is out of bound
. ]; O. C6 P! _, r& c/ W; c{
# d1 r$ K8 d& P% ^+ LSystem.out.print("无此编号的数据,请重新输入:");  7 D1 w6 S. q$ a$ L6 S4 w/ Z6 I
getid(count);
& A) D, v) o$ h6 ^( g8 X2 R}
0 ~  T0 }9 U# z" K1 creturn value;//return a value  $ T0 n8 d0 D# t1 V# D/ G1 l
}  ) p2 P- t$ _: }& @7 ?$ C
}