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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);
  G, |/ i0 o- R. q# w! JSystem.out.print("
6 {* [- s9 l' z' ?6 s9 T8 {目前共有"+count+"笔数据");  * a6 }. l& N* o9 x/ D# C( s* c
System.out.print("
1 Z; Q; Z  E1 o5 F! ^5 u# ?: i4 C
按任意键继续...");
6 X" D  r: P" U* Penter=bufin.readLine();
- `* j5 {6 K" u; W9 q# Z# Q( Znew str14(htable);
; k- f* `, b3 A( Cbreak;
( L" c3 Y  T1 ^6 Z( b5 g4 Zdefault:
2 Y2 D+ b5 U% s9 V% ^}
/ a8 K  a8 w. }9 f0 o}  0 Z8 J7 w8 u3 P# j' f* l

/ c2 d+ W: o" Q: Ypublic int select() throws IOException//method of getting a function selector  7 m* Z# g% ]8 S% F
{  * U% e$ q- h2 C0 h6 C/ {$ L0 Y) ]
String input;  5 T$ s& q. M5 |2 m( x+ l1 f
int value=0;
7 a1 I9 m/ @% c: Winput=bufin.readLine();//read a input from keyboard
3 B6 L( w1 `5 X+ n' Rtry
- w5 P$ |; I7 `  `. Z; @' a2 c{  " k8 E" O* K* J- A  X/ {& O$ f: O
value=Integer.parseInt(input);//convert a string to a int value  & P+ y2 @: W& e9 [
}catch(NumberFormatException e)//can’t vonverted  4 V& A/ E" a- e8 j* ^, E; G
{
: V' F* v* E. N8 U6 QSystem.out.print("请输入选项1~6:");
! c9 a7 G6 n9 f( Y/ Rvalue=select();
5 V2 h3 v. E, d$ w; r, j& Q, v}  $ ?+ }4 t1 X1 W* w9 u4 h2 }9 D
if(value>6||value<1)//if exceed then print a message and reenter  & l4 Q6 a0 ^( F$ E
{
- {: e4 t4 C9 r3 g. bSystem.out.print("请输入选项1~6:");  * O3 \2 U5 U, t- R4 H
value=select();
8 {* ]+ L" V1 F}
& W6 {: i' m, Mreturn value;//return a value  2 X& B3 x. P/ }+ R2 k( ?6 [: X
}  ( W$ l6 A: F* q: z! T

0 @/ X# p* w9 @; `' Cpublic int getid(int count)throws IOException//a method of return the number of data
; K- X" @, O) m! ~$ @{
. O. l. M' Y3 a& v& iString input;
5 f( ~: T5 r% T' {* }; ^# p0 fint value=0;
8 ~; C' y' [, }1 tinput=bufin.readLine();//read a user input string from keyboard  * r3 n3 i# H! c5 T
try
; M; M0 z6 Q) F8 d{
" s# u" N, E7 ~7 t, y; @  \4 Tvalue=Integer.parseInt(input);//convert the string to a int
  q) M$ u( d& C2 c- n}catch(NumberFormatException e)//if can’t convert to a integer then reenter  & ]" Y/ E2 \' N5 q5 o4 C0 n7 z8 j
{
7 T  e) L1 ?$ e. H8 a* VSystem.out.print("请输入数据编号:");  - ]' \3 k  K2 \, U1 W/ t
value=getid(count);  / u* \; Q' a: _# i! g5 [4 Y
}  - L7 _4 d4 ]5 J9 W8 [7 e
if(value>count)//the input value is out of bound
0 c& `6 o; n) o7 Z3 n{    `5 N' U  w( G( f* q% u) m/ X
System.out.print("无此编号的数据,请重新输入:");
- E4 k* h7 C" E: m& \" u* ~& X. ?getid(count);
: W' M5 v6 f8 I. ?# C2 ^}  1 g0 e. J4 D. K' ]7 r+ m" S: o0 [
return value;//return a value
, o2 ~8 \5 x& k}
1 u8 D& a: b6 T+ r}