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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 |正序浏览

|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);
+ s1 K3 s9 Q% WSystem.out.print("0 ?9 C2 w, X3 `1 V+ n9 i! F/ {" i
目前共有"+count+"笔数据");
" G" q' `5 u3 ?) c$ ?7 H& JSystem.out.print("
) ~9 E& @9 g# n* s
6 j( t- C' W! j3 I+ r3 X6 E按任意键继续...");  : m6 S& O8 L! q
enter=bufin.readLine();  - s. g: _7 g6 a
new str14(htable);
" e& ]" h6 [; _$ Hbreak;  # B/ X7 g$ R/ L: R
default:
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! ], a1 g3 n$ o( A% y) U$ Z/ T  Jpublic int select() throws IOException//method of getting a function selector
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String input;  * I" V/ S7 u1 c( l# i& v4 ~
int value=0;  " U: q* C2 d2 B" h: l# K0 U
input=bufin.readLine();//read a input from keyboard
0 z8 ]! x8 d2 m, g" x# J$ p4 Atry  + `7 G0 h% M& j4 V# I
{  8 m8 Z2 {8 |2 B2 d" T0 p+ V" m4 x
value=Integer.parseInt(input);//convert a string to a int value  + S0 Q( m% a7 f$ h" Z
}catch(NumberFormatException e)//can’t vonverted  * J+ t) ^5 g5 G% w9 a
{
/ S7 P0 S7 m" T# NSystem.out.print("请输入选项1~6:");  7 z, b7 W4 ?3 W' E6 `
value=select();  2 |$ w# t8 N1 t7 r0 O1 m
}
6 \# E, {: l- c' S& xif(value>6||value<1)//if exceed then print a message and reenter    E2 n2 `/ f& f
{  . Y! _* B4 h1 f% A% n
System.out.print("请输入选项1~6:");
) m( ~3 f, C$ @! c) ~& u  vvalue=select();  6 M" B/ K$ d+ k
}
- v: w# H9 Q& _: Treturn value;//return a value
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public int getid(int count)throws IOException//a method of return the number of data
/ ~- I7 D) D# `4 N9 ~{  ! J) u6 m0 K. l, l) Q$ t& Z9 Z
String input;
& R1 D% _7 T& A' a7 |int value=0;  5 r0 [( O: I) z  h1 D
input=bufin.readLine();//read a user input string from keyboard
, r/ l! E  j3 v1 y4 D0 D) Q' _0 `( ~try
8 \2 H" }- V! o3 y9 f( O* Y; X{  ) s! z# a" t1 C7 a
value=Integer.parseInt(input);//convert the string to a int
$ h+ A& ?0 x+ S, t/ h}catch(NumberFormatException e)//if can’t convert to a integer then reenter  & c9 y' I) x" q
{
. c' T4 M" a6 q# ?: F* C& iSystem.out.print("请输入数据编号:");  ( y8 o; d) d9 C
value=getid(count);
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if(value>count)//the input value is out of bound  5 w+ G! P6 h7 l; m
{  9 W- ~( D# l. S% B6 z1 ~4 ^2 ?
System.out.print("无此编号的数据,请重新输入:");  3 b7 K( }2 m; u( ~1 P1 W2 F0 x/ ^6 Y
getid(count);
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return value;//return a value  ) R7 }6 Y( {' L1 a9 ?' B
}  6 J9 ^. F; G$ a, B0 l: W; H
}