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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);  * {- a6 f8 G* N8 m  _* I7 ^
System.out.print("1 v5 D* F; o& J- U
目前共有"+count+"笔数据");
; ?5 _8 T8 i4 p: k" X" I$ n6 P, w( ASystem.out.print("& P! R5 i( z- m. b9 z5 M5 |
9 H7 r; O  ], o/ E0 f! J3 j5 u
按任意键继续...");  7 c6 l( C) _. S% L. b* T
enter=bufin.readLine();  4 ^/ N7 X5 s) h6 W0 ]4 S  Z3 S4 R
new str14(htable);  4 R; K8 {& j4 |
break;
6 {. ?1 k( j- n6 H9 X# ldefault:
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$ N: _& q8 ^3 a( |; \
/ J. \9 W7 d" F2 u) rpublic int select() throws IOException//method of getting a function selector  8 X1 l/ ~+ L+ @
{
8 a) z1 w* f4 A& V1 lString input;
- c- D6 e7 y8 k2 c, U$ x: Zint value=0;
/ Y" y, R6 o7 Cinput=bufin.readLine();//read a input from keyboard  , A# c& s9 C% m$ @& Y3 ^
try
# N' @" Q5 ~9 U' m+ A+ w+ G{
" ~: l6 u% p( I: C& N4 F3 ~value=Integer.parseInt(input);//convert a string to a int value  ' t+ P6 g6 f$ ^7 Z$ V6 k" G
}catch(NumberFormatException e)//can’t vonverted
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System.out.print("请输入选项1~6:");  + g0 ^, H/ h9 A# q* J
value=select();  / ~1 c+ n  A8 ^/ V6 Z
}
6 u# I/ _$ @: o8 P; o- wif(value>6||value<1)//if exceed then print a message and reenter  : c3 ^5 @  w# }* i# ?$ {) W, ~! A6 s
{
( M% q; _! c% M1 ^3 ^  o* b/ k2 q9 ESystem.out.print("请输入选项1~6:");
- H9 q& k) R2 y2 `- ivalue=select();  ! Z1 }' v. R: r- Y8 n1 y4 E7 w
}
# L& R& b- p% u3 ~2 {3 Qreturn value;//return a value
% h2 |6 `1 j' `/ i# t: y4 r; }}
- c8 ^- ?$ s5 n
8 d+ E6 p  D' S2 Mpublic int getid(int count)throws IOException//a method of return the number of data
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0 B1 p( e# m2 t- Q% nString input;  ( [# D9 E+ }% r8 s
int value=0;  ) k' a& ^( w1 S0 o. e" g
input=bufin.readLine();//read a user input string from keyboard
/ `# d' I/ p+ v& `4 ztry  + O3 F( O8 K/ c' J# Q8 V
{
* }9 `) F9 N( Z5 x: Y3 {5 @! Fvalue=Integer.parseInt(input);//convert the string to a int  7 r9 Z% u2 h" A0 b
}catch(NumberFormatException e)//if can’t convert to a integer then reenter
! O2 y2 }8 [4 E{  % \3 Y/ ^9 S  J- U+ R4 v6 ?
System.out.print("请输入数据编号:");
% e% p( H7 s0 u1 Z: b$ H! `value=getid(count);
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if(value>count)//the input value is out of bound
* a8 U, b1 e' O9 s5 N% Q6 P{  1 z- M) B1 `$ D3 g  D
System.out.print("无此编号的数据,请重新输入:");
! y  r+ S9 w6 Z# Vgetid(count);    ^( p1 L! S$ r# N# v
}
" m3 i# x( l" v' G9 P- X2 kreturn value;//return a value
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3 B2 x! U; s1 ~# L6 y& V$ o}