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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);
/ ?$ q6 D' T  }& F* x3 HSystem.out.print("9 o( @4 u  p* L, I) \& r# W7 g
目前共有"+count+"笔数据");  4 B' q; _' B' @) C/ B
System.out.print("
& S/ W$ y8 I$ u+ ^- h+ m! y1 y2 Z: Y  Y: I0 C
按任意键继续...");
7 J% W( i7 Y, U6 S5 T! yenter=bufin.readLine();
7 @% D" x, J5 W. Z) P6 K( ~new str14(htable);  " F# M5 m& G# ~8 M5 v
break;  # j! A! q  t) J# c
default:  * S! z9 ?7 B4 b+ G# }
}  $ q+ H9 |( [+ ]9 c. O, @$ q
}  ( T# y' |" u- l' s* _  i/ T# m) d

! q' _2 r  f7 w  v% `5 t; L' [public int select() throws IOException//method of getting a function selector
. z+ X$ R  u" U{
# v5 p& R6 i0 K1 w# Y$ g- p: `String input;  ( U8 k- D( |' u) o, m( n
int value=0;  & @; c( D3 [5 ]8 T9 T
input=bufin.readLine();//read a input from keyboard  1 ^2 H" O3 D4 H4 }. y
try  3 Q; H) Y8 N4 a$ l" L
{    L0 m8 y& z2 b# F; j
value=Integer.parseInt(input);//convert a string to a int value  9 O* c/ P8 L/ P& n9 H7 G
}catch(NumberFormatException e)//can’t vonverted  . y- O) _7 }1 ~- _# K
{  4 ?+ ?: I+ o7 l; Z. u
System.out.print("请输入选项1~6:");
  F/ r1 G' |& V* v( Vvalue=select();
* c9 C& |" T# R}  " m& E1 A) Y# B$ @5 Y6 G- v! c- @
if(value>6||value<1)//if exceed then print a message and reenter
( p; H' d4 N4 h, Q; l{  % M: D. Y, S2 ~  R0 ]
System.out.print("请输入选项1~6:");
- z3 h0 c! I) @value=select();
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return value;//return a value
8 m+ r' g0 N+ n}
2 B9 ]: R1 y* _# b1 i. O' b+ U& ?  S0 `) U3 j6 P
public int getid(int count)throws IOException//a method of return the number of data
- i$ v- D) k$ l) i# |: X{  9 ]$ l7 @4 y9 \
String input;
, f1 ?$ k% Z+ E: @$ s0 O+ }int value=0;
9 k8 F, i. H6 V0 }) L; Finput=bufin.readLine();//read a user input string from keyboard
( ^! a9 F9 v" T7 rtry  4 X. K, _8 w$ V3 k# d; p
{  , L. v3 u3 c8 V+ k( |1 w
value=Integer.parseInt(input);//convert the string to a int  2 |3 J2 g/ D  X8 @$ \
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  0 }5 z8 ~* ^0 w4 n: a/ S
{
/ l6 S3 @( n& q" u+ C* q' K& wSystem.out.print("请输入数据编号:");    L6 {; f  f% j! D' A7 [4 Z$ w
value=getid(count);
4 y  L. [* P. y1 `, ?& r* J}
* L6 I/ \3 K7 d6 S5 w6 j) d6 lif(value>count)//the input value is out of bound  & `+ D( R6 x. t) R8 k
{    C5 v2 e. ^$ {! V- o! M2 u
System.out.print("无此编号的数据,请重新输入:");
+ p' ^$ D" v& L% z5 Y& k& Dgetid(count);
" N- j! g! W, ?. R3 T( l}  6 l) z* m5 M; `4 d5 R- G# h$ Y
return value;//return a value
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}