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标题: [转帖]Hashtable简易数据库程序 [打印本页]

作者: god 时间: 2005-3-31 01:45
标题: [转帖]Hashtable简易数据库程序
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 G2 M" }  p+ n8 R: a0 t3 ySystem.out.print("
7 I2 e( ^1 k" Z$ v3 P) \目前共有"+count+"笔数据");
9 j# F6 ^5 ~# r+ G- M: V7 J: W; b  gSystem.out.print("
" N$ A: ]: @0 z3 O* j& r" B  D  H. A9 U* {
按任意键继续...");
  p% e$ L' A. @3 _1 S( f8 a0 zenter=bufin.readLine();  2 v9 U* Q6 A6 G8 }. ?+ S9 H
new str14(htable);
) m0 r+ `6 T# A# F, P8 k$ [break;
' G5 S, C/ {6 b: q8 d$ Vdefault:
. K, ?0 t' Y; z6 E/ p}  , M" @( R; z) d, v5 T# v: S
}
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% D* @, ]+ Z" u( G! f$ S8 `public int select() throws IOException//method of getting a function selector    n! }, c' w; B& C" {; ~) l: q
{  / n8 r% |9 k3 f! d% C
String input;
8 X+ j: P, ^5 l' o  R, {( D  yint value=0;
& S% V- i. ]3 E8 ^2 H  U, Vinput=bufin.readLine();//read a input from keyboard
4 v9 W! f" q4 j( b8 q& `- jtry  $ c& u$ H# X6 I* i- k+ Y0 Y
{
4 g, P& Y! L' o  U" _( g0 \5 k! Qvalue=Integer.parseInt(input);//convert a string to a int value
. G" g( B3 O$ n4 U6 F}catch(NumberFormatException e)//can’t vonverted  4 B: ^/ e$ e9 ^  u3 H
{  . p# U8 Q$ [/ C
System.out.print("请输入选项1~6:");
$ |6 u/ J% I7 C  X( Wvalue=select();  + q- h* g# ]1 `' P% c- k9 g+ ^
}  $ F) `# b! u$ O7 O, L
if(value>6||value<1)//if exceed then print a message and reenter
( g  n2 {, g- M  Y5 T6 U, F{  ( h1 M- f( w  H2 `- d: Z
System.out.print("请输入选项1~6:");
( J2 ~2 ^" T2 ?0 `0 kvalue=select();  2 r' \# S+ k2 k- V) u
}  9 W# _% ~. U9 N( P, ], W4 N
return value;//return a value
: |0 @' w  y, I; U7 q& b}  8 ^8 D% U- k/ Z8 h

4 F$ O/ t3 r- @% Qpublic int getid(int count)throws IOException//a method of return the number of data  * P, Z. j+ {; c0 S4 l
{  " I) T7 o) u" T4 k# i: }7 Z
String input;  / e; [4 N0 |6 ?0 @* ~4 w$ Q' E
int value=0;  - {3 n$ s8 T8 y4 m% z; v
input=bufin.readLine();//read a user input string from keyboard  - L0 ]3 U. L  ]3 {# M
try
5 M9 `7 Y0 N$ b2 G8 c; z{  ) L, Z" h8 o. e$ G4 w
value=Integer.parseInt(input);//convert the string to a int
- O0 R$ O. [; A6 z}catch(NumberFormatException e)//if can’t convert to a integer then reenter
9 r# w8 F3 j- P7 x6 @& S( L{  0 _* N: `7 |9 S+ a; }3 S
System.out.print("请输入数据编号:");
; V$ f  U. ^9 u" U9 Zvalue=getid(count);  ! s. p3 N5 k& U! ]
}
' k8 W' y* H! ^6 P9 [- f# O( hif(value>count)//the input value is out of bound  + D' ]- l  _  w2 T0 K. `4 q
{  1 |& l- C  q0 e! v7 J4 N
System.out.print("无此编号的数据,请重新输入:");  " w" e9 V$ U6 S9 f: K
getid(count);
& ?. W% v/ W% M/ X. h! u}
+ ]& X) v3 Y0 u( Ireturn value;//return a value
8 W1 b1 b/ z" V6 p! l}  . J, x8 D' ?/ c3 G% M/ l
}

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