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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);
. \4 t+ x- F, f, K0 [System.out.print("
1 X0 v, ^. W. R$ l$ k0 `0 Q. C目前共有"+count+"笔数据");  , _+ D$ T; \$ ]/ r
System.out.print("
' V3 x$ u6 q! @
3 s4 Q5 E: V- {  k1 J按任意键继续...");
* T  |+ L" K; e0 B% w* ?" Uenter=bufin.readLine();
4 y" b1 ?+ t! _- }  J, Wnew str14(htable);  9 H+ a( N- q+ V+ L; ]5 n
break;
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}  / k& z/ S* U7 M/ `! C
}  $ X3 Z/ h( B" n) y) L5 f

- [* H, P! W! E! ]: Y; Tpublic int select() throws IOException//method of getting a function selector
* I$ t/ C6 l" e2 r7 R& v{
& L* C5 _. o% n, A+ W4 U: [String input;
9 R# |9 ?! n0 O: Lint value=0;  % m* N$ |9 L. K0 P/ N
input=bufin.readLine();//read a input from keyboard  3 K; `. B, @( y' F, O6 \* C
try
! d5 t1 E1 T2 s, b. X1 q; m, m( r{  6 h5 X8 V* W5 v* P! v
value=Integer.parseInt(input);//convert a string to a int value
: p* ^  O  k4 M5 y" p2 ^}catch(NumberFormatException e)//can’t vonverted
, b" @# _+ t4 L4 r# i{
! }4 |; m3 R( _1 E' X; e1 c1 ^System.out.print("请输入选项1~6:");
% P" I! D; L0 N# u" @% s( j! h$ ?7 {value=select();
6 _. w8 g! g% O/ e2 c) L3 b}
3 \) L/ ?( i( p0 [3 l& c' h  hif(value>6||value<1)//if exceed then print a message and reenter  ; h. j" s4 b6 K/ C0 |
{  * l* O1 }$ ^* z7 W- ^: s9 S7 E- u
System.out.print("请输入选项1~6:");
5 a1 y0 a1 e9 t2 avalue=select();
! f: G* m' a& H- G7 R}
6 z% [" z6 b) Breturn value;//return a value  6 w! b" Y5 b# n1 ^% k7 C( W6 J2 X
}  : m) r, ^7 ?& k5 h6 t
# h) o; d$ }& ], e& C- J
public int getid(int count)throws IOException//a method of return the number of data
; n* F7 H) ^% _& k{  . a, G, i  {1 E  ]6 Q& K
String input;  5 r) o( ]- z. i/ O( [: [
int value=0;
7 g6 v; X) y7 _* Winput=bufin.readLine();//read a user input string from keyboard
/ V. E8 q1 ~  H, y7 m3 D0 Ltry
) P, y' Z) l* G) W" i{
! p: H9 y/ Y! U% q# F) ]. \value=Integer.parseInt(input);//convert the string to a int    |" N  ~* {5 f, x; @+ k
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  9 y8 G8 U6 J2 w/ x. E  l- @0 k
{  ! E" C' T& ~5 d4 V! T) E% B6 J* F5 \
System.out.print("请输入数据编号:");
8 l( W3 }6 u9 M3 R6 ~value=getid(count);  7 A& e0 q" d9 |1 N
}  " A; j" |, q" B/ ]8 N. [
if(value>count)//the input value is out of bound
9 @- Z, `' I8 ?3 L" P, Z5 H- z  F{  ; U' J! t- ?, T8 n2 L
System.out.print("无此编号的数据,请重新输入:");  5 ~9 @& N& b1 w1 q1 F
getid(count);  2 I! Q0 [, u0 l
}
, E+ @- H, p1 D( S/ k% H: L1 v/ Rreturn value;//return a value  3 Y6 o5 K3 d' _) l
}    Y: G' G9 L2 U
}