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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 c3 I2 t6 T4 Q! USystem.out.print("* J, `0 z) r) D; w9 m( _
目前共有"+count+"笔数据");
( [- |1 p& D2 T0 z7 V2 eSystem.out.print("/ l' D$ i! x& ?3 R9 t' T3 g

9 X2 n9 ^: c' P+ v/ @" B按任意键继续...");  & k! _# z6 m- ~" c0 O
enter=bufin.readLine();
" _& b; E( S- M) W" Ynew str14(htable);  + G6 {. k  P4 q0 K9 n6 L
break;
/ N5 t: X* J; c+ m3 A2 O/ G. Zdefault:
( o* ]% |; n, t3 g/ i6 w! ^* \}  # A. V) M3 @9 [0 ]7 z
}  5 @( E1 z/ q& }7 v5 e; K
8 ?! z( H0 h* f9 i
public int select() throws IOException//method of getting a function selector  * o# F* V( z3 C; i! W2 k
{  0 E0 T! M8 k8 H
String input;  # W5 ^; C+ [$ i( m: A
int value=0;
# x9 L8 i6 b  |( ^# yinput=bufin.readLine();//read a input from keyboard
  E& @0 T- g  K+ T" t# btry
3 [# Y- g8 J! v" O! V9 P$ j{  ) h; A1 w! d/ c7 O& k2 B( c
value=Integer.parseInt(input);//convert a string to a int value
' Z! f/ e" A6 ?+ N4 u2 b}catch(NumberFormatException e)//can’t vonverted  % u* a" s3 p8 J
{  + a; e- E" d' d' D
System.out.print("请输入选项1~6:");
, H7 \' s5 A7 d& P$ {: ^2 P& {value=select();  4 t/ A1 d8 s- y& {
}
6 D0 d$ q4 o, {) x& Rif(value>6||value<1)//if exceed then print a message and reenter
5 [7 v) S* K" ]- g( Y) v: s{
; x: c# H7 [' V8 S. L, b8 m+ P8 BSystem.out.print("请输入选项1~6:");
5 i  K  O1 t+ q; K4 U  bvalue=select();  % O: F9 ]6 {: M  @
}
5 |( p7 H% S0 b5 b6 {5 Sreturn value;//return a value
& Y5 h- x- p. y5 C& `% ]! {}  % {7 H# l4 o( X4 S' l/ T4 }3 n
! w! f9 G$ M" V9 N" N% h
public int getid(int count)throws IOException//a method of return the number of data  8 R6 Z7 Y; A. R( K6 S6 J
{
- O+ v5 a& o8 s0 uString input;
9 ^$ L! S/ w4 F  u; p8 r' mint value=0;
0 b/ J; P+ p# ~6 |4 x" W. f% a3 uinput=bufin.readLine();//read a user input string from keyboard
+ x9 \, A2 R+ a& Wtry
7 o+ |; |" Q$ Y{  / _5 `* J5 F$ U' ~
value=Integer.parseInt(input);//convert the string to a int  , }- s9 {, d' f
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  6 b8 k/ _5 H" e! n  o
{  1 O% z( F3 T) G- [. [8 y( O
System.out.print("请输入数据编号:");  + c( t; D5 i1 V: j9 a- }" n
value=getid(count);
) m4 h6 p9 t+ ]0 c2 R5 C' r4 _}  9 S0 O6 x$ {5 L7 R
if(value>count)//the input value is out of bound  # c, z4 R5 T6 S/ c' ?
{
- O( Z# `% L- n# A) w" iSystem.out.print("无此编号的数据,请重新输入:");
' E1 I( J5 ^% egetid(count);
+ ^0 A+ ?) M' X! `}
8 [% ~( H6 _, Oreturn value;//return a value  9 `3 ]& G- e0 V* c* X5 O9 O
}  # n7 u% X- _. I( E1 n% n) [
}