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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);  % i& O& O9 c, Z6 _& P3 J
System.out.print("
/ V- |- ~3 m% N+ J/ q* f! \  x目前共有"+count+"笔数据");
, j- o% y1 d7 q6 XSystem.out.print("
) {1 w  w# b; H/ U6 D4 p( w1 ]$ @0 `3 u, _+ ^  |! N' N
按任意键继续...");  $ {  {; f0 D" ^3 P  R/ B, I
enter=bufin.readLine();  2 |. K+ o* F% p  ?. _; V% K
new str14(htable);
) V: s2 O4 l. k) ^break;  ; d% E. j9 E+ {
default:
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}
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public int select() throws IOException//method of getting a function selector
0 n. c0 E: y3 R0 i' i; Q1 Q{
+ _: _( A2 K3 C6 IString input;
% Y( X5 X6 J+ {; l2 i* {int value=0;  - Z& `$ \% }0 p' G
input=bufin.readLine();//read a input from keyboard
7 B! O& J  G* Ktry
* K% w/ a8 _3 m& X- S; \' }% B7 w{
9 t1 d# y' b; |# x  G, Avalue=Integer.parseInt(input);//convert a string to a int value
1 p! o( a, ^. E! t( c5 b}catch(NumberFormatException e)//can’t vonverted
' H" x0 l- S5 [. {( b{  ( d& n2 `6 v; f. R+ x
System.out.print("请输入选项1~6:");  , t( k  I, l8 T# l3 B
value=select();
/ V! g9 f8 B' a6 C/ V% f& r0 B}
) [; e5 l) ?4 p! ]. v, v5 iif(value>6||value<1)//if exceed then print a message and reenter  2 _' X; M- v9 I* j: `
{  7 D& M' @4 U) r, s% {: E  h1 W
System.out.print("请输入选项1~6:");
2 S  S- Y* K$ s% {value=select();
* X6 G# b+ h1 u4 e1 r4 I  x1 S}
  p4 K5 i9 v0 h" f( K1 s! ^return value;//return a value  , r% B' A. q  i- l6 |& l1 b
}  ; H0 t# b2 }& ]% _. h1 P' a. Q

9 u. T: G# r1 f2 Upublic int getid(int count)throws IOException//a method of return the number of data  5 I8 D, E. Y4 S( t3 V4 \
{  8 s7 f2 a, F( Z0 C. A% j) X, x
String input;  7 I# c% u% _- j/ G- R
int value=0;
. {" l0 {: ~, y1 ]input=bufin.readLine();//read a user input string from keyboard  # v8 S$ n$ E4 ], b
try  - Q$ b; }9 @- |: g& T
{
, c; U" F# X% A- B: Nvalue=Integer.parseInt(input);//convert the string to a int  4 D" f6 B! e+ Y5 w( N
}catch(NumberFormatException e)//if can’t convert to a integer then reenter    W: E4 @( Z3 p8 ^9 S
{  0 a, y$ L' u3 c6 g; p0 B/ \  m
System.out.print("请输入数据编号:");  # i* M# d0 t2 \& [0 q$ Y& ]
value=getid(count);
0 X$ f2 q; N- i7 O- F9 X% Z% `}
2 @5 v5 p9 E7 e6 eif(value>count)//the input value is out of bound  # j% q' |7 d7 U2 q7 a% ?: x, G, @
{
8 y2 i9 k1 {3 ~' {; Z' f8 \' o7 `+ CSystem.out.print("无此编号的数据,请重新输入:");  . G! F$ V8 n4 }
getid(count);  1 f9 ~' D3 K. F$ L
}
; T) g1 G" @! q0 sreturn value;//return a value
* r& i; ~" W. m: Q}
& E; P( i* h2 `& C}