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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);
) D5 A# c+ f% g, \9 T  ]System.out.print("
6 f  [# l! H# H6 E目前共有"+count+"笔数据");  & B9 u' a5 S* l! I* \
System.out.print("
! i6 K: i! N, E1 D5 L2 Y0 L, S% I6 t% u- c- A
按任意键继续...");
2 @$ j2 O! y1 r# C: Qenter=bufin.readLine();  8 n# }8 W: F: f; y; f' z
new str14(htable);
& f6 x( w, n3 s$ K$ [, g, Xbreak;
: K6 O' E4 A8 E5 c/ v6 fdefault:  $ f  ?2 o0 h5 A# b. T0 }2 W. H8 [
}
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+ M# @" |# U: x' v1 P
public int select() throws IOException//method of getting a function selector
& }; w+ h- ~9 F: m# u9 \5 p{
3 H) {7 e5 ^: t9 h  PString input;  ) [  A5 r3 B$ N8 M" S
int value=0;  , S! }6 B( o' m- z" Z8 l
input=bufin.readLine();//read a input from keyboard
/ l( z! K; F* itry  4 S% B( U, L$ d# P$ g* t% e
{
- b# c7 N8 j. O( e) svalue=Integer.parseInt(input);//convert a string to a int value
. [# {& P8 u1 Q. H* ^* n$ V6 s}catch(NumberFormatException e)//can’t vonverted
  i) V0 `" }5 v! D) Y9 m: z& @! i{  9 ~7 j2 T4 o. ?! Z
System.out.print("请输入选项1~6:");
- L4 m5 l+ h( c) }, s2 [) e6 q' Svalue=select();
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if(value>6||value<1)//if exceed then print a message and reenter
7 ?( @' s: M  N{
2 s  C3 P% n! C% v8 w6 [System.out.print("请输入选项1~6:");  - I( y- S2 |4 U! r) c1 ^5 a9 m0 d2 H
value=select();
, @# J+ p6 @2 g5 i- I4 o6 v}
8 t9 H8 X+ u+ x: qreturn value;//return a value
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! B3 G& k% V- xpublic int getid(int count)throws IOException//a method of return the number of data
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String input;
" C7 }$ b3 N8 u0 S5 X6 hint value=0;  1 R9 a) |% P! }( o0 M$ A: [
input=bufin.readLine();//read a user input string from keyboard  6 b$ p# d- k* u
try
; N3 x0 ^4 V* c) Y+ J# e& L0 C2 X{
4 ]' V+ [2 a7 [7 Rvalue=Integer.parseInt(input);//convert the string to a int  5 Q$ {8 t& c, w2 Z
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  , w! e$ ]. ~2 F. _  s
{
0 x6 J" O( Q9 L, u  ?2 ?System.out.print("请输入数据编号:");  $ p9 }" C/ m# y- D& {) p, A
value=getid(count);
+ ~; j" u% S5 c$ ^% Q7 L8 \' e}
$ Q) `9 s4 |( uif(value>count)//the input value is out of bound
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System.out.print("无此编号的数据,请重新输入:");
$ r9 Q! j% l" ~) U$ ?% E1 Ngetid(count);
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return value;//return a value
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}