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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);  1 k) ?8 n) A& B+ I
System.out.print("/ q, C! d1 a- N& M* r$ m
目前共有"+count+"笔数据");    a& r4 S9 I4 o, T
System.out.print("2 [. h6 h& c7 Z0 K3 c0 }
, x! Z3 q- y) E6 `1 J1 G
按任意键继续...");
# j7 @$ u, B1 ~' j# `enter=bufin.readLine();  ) B* U% O+ _5 _6 p
new str14(htable);  8 ]0 V; n8 t9 Y" ^7 e* c# _
break;  , I6 F9 u; l& V7 v- {
default:
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}  7 U- {8 ~& H" C0 U0 k6 {& A5 U! J$ o3 h

3 t; S  q4 T* k5 N/ B% C5 m" Tpublic int select() throws IOException//method of getting a function selector
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String input;  . N3 V+ l. k- r  N+ V+ z
int value=0;
* `) g- }) J* k  ^input=bufin.readLine();//read a input from keyboard  ! r: Z8 Z7 ^0 f" r& _( M% o
try  * t" _6 \- |4 Y0 L. e8 j! c
{  7 x1 P4 s4 w3 m3 T  X. a: ^
value=Integer.parseInt(input);//convert a string to a int value
% W3 V) U# Q1 r/ `" C, c, ~}catch(NumberFormatException e)//can’t vonverted
# F4 O) z, P: S: y  a& F{
7 [  ^* Q6 N. LSystem.out.print("请输入选项1~6:");  1 O9 K, ~5 L, w* L6 ^9 b+ @0 I+ r+ @
value=select();
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if(value>6||value<1)//if exceed then print a message and reenter  3 Y& ]+ q3 @% R1 N
{  + J7 [9 v* C3 ?; ?
System.out.print("请输入选项1~6:");  ' `( E# [6 {. k& T& `% M" t/ N
value=select();  4 t- R" d5 ]" h6 f
}  $ ?7 Y7 n" g4 ^
return value;//return a value  2 \; p  T4 {/ ]0 C& Y7 B
}
; |4 S' c" D) C6 \
7 B( C0 w" k1 N5 ]0 R  o0 v' J3 Vpublic int getid(int count)throws IOException//a method of return the number of data
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String input;
* a0 r4 D1 Z/ @int value=0;  ' G4 w. \1 |7 w5 G$ O. V/ k
input=bufin.readLine();//read a user input string from keyboard  ; j1 ]8 m4 y/ r2 O
try
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value=Integer.parseInt(input);//convert the string to a int  9 l$ E9 k4 Z3 A3 d5 S# |
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  . N- |4 K4 _, Q( i( p2 r8 k) o! t
{
& r1 A' ?; b6 fSystem.out.print("请输入数据编号:");  ( I* w5 f1 ]( v, W% }2 @$ D
value=getid(count);
+ ?9 U$ u* I  B" @}  , z+ j/ q) i! K$ ~% N- w
if(value>count)//the input value is out of bound  - q6 ^1 j! ^) H( y5 h! G8 P8 U
{  0 q& D/ x/ b, v! N! y
System.out.print("无此编号的数据,请重新输入:");
" I- a6 t! P; w3 }getid(count);
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return value;//return a value  4 x& |$ _8 M& E8 q0 I: {
}  0 V5 Z0 h- l1 r; \( ]
}