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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);
' \# q" o4 k, rSystem.out.print("
! a. F# W8 u$ r+ s目前共有"+count+"笔数据");  ' L: B  j( I& `" K- j
System.out.print("# @% I$ a) `! n- `) [0 q' {
  @' z  X- W7 w& R2 ]% r- O
按任意键继续...");    L+ ]/ k8 P7 C9 {
enter=bufin.readLine();  8 [8 i6 Q1 A. e: }" _
new str14(htable);
! L& F) l2 W- Kbreak;
+ z- S2 G, y" s1 d9 M4 W6 X. x0 ]" I. vdefault:  % A8 s5 Y! t/ ~1 n& z% a' Q
}  & s1 z" A3 u7 h# C* y% B2 b
}
( T" i+ x) s- g: J- y/ \! s2 a$ [3 o
public int select() throws IOException//method of getting a function selector  - {  F1 _$ ]9 J' X5 k. S; H3 r
{  & `, i2 D& Z/ i& c6 g& ^: M) |
String input;
% R" }: l3 j4 F; Y! aint value=0;
, c$ q  @) @! U8 O  I  P3 Ninput=bufin.readLine();//read a input from keyboard
, Y  h. V" d; [( |; E' wtry  ) e' S) S' z5 C9 {* w7 |
{
9 a' D) K( E; y. p) ^0 @value=Integer.parseInt(input);//convert a string to a int value
  T$ Y, `, F) X}catch(NumberFormatException e)//can’t vonverted  & |3 S6 O# Z) s  ~$ `
{  " R  ?1 ^. A; a0 D, `1 e
System.out.print("请输入选项1~6:");
8 g/ D4 T! @* G) l( M$ N: O# l& hvalue=select();  ! r6 h0 M5 ~( k& L$ v9 _% Z' F4 \
}
: v! J4 |; `' Y0 J( [" \if(value>6||value<1)//if exceed then print a message and reenter    k7 {5 T8 H2 P1 E  h9 }
{
7 X5 w! P: R9 [6 J) Y0 G& NSystem.out.print("请输入选项1~6:");  . V, Q; O* t$ b: e9 I3 i" I" o. P
value=select();
2 B% t- w8 q. g% Q* j) b) |  b}
+ b  h- c) ~3 G: ]& d3 Jreturn value;//return a value  ; G% {3 ^% T- ~& K* B/ p
}
% N1 L+ T5 ?/ @% B8 }
+ b" z2 @) A7 y' m- B: mpublic int getid(int count)throws IOException//a method of return the number of data  - J- S. _( X) e8 {' K
{  ' i$ W  X6 e" G2 h
String input;
5 d) k- o! p5 {1 W) d3 ^/ W4 S7 vint value=0;  & k" I- ~" |  G) M
input=bufin.readLine();//read a user input string from keyboard
+ G& v$ n, c* ~$ T: m! k; Ptry  & s3 R/ t: p# w0 D3 B+ w3 h
{
9 G# R& _9 k& _value=Integer.parseInt(input);//convert the string to a int  ; r  K) W  T* Z( {
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  : R& p+ ~5 j& F; l3 y- W6 S
{  0 b" J, K7 L* Z4 h
System.out.print("请输入数据编号:");
( `6 L; t4 w/ i6 i3 @value=getid(count);
! @, F2 w) J# q}  . B3 `. j  U- T/ Z0 S, z- P
if(value>count)//the input value is out of bound
2 t" O2 h* @, R; Q{  $ E+ C4 O- @9 ~- A9 K( [
System.out.print("无此编号的数据,请重新输入:");  8 a7 {* D1 o, H* t" [3 l; j
getid(count);
- X, ^8 U. c4 i4 {1 m}
- S" f" s# V+ i1 m( g/ P' }( b* Oreturn value;//return a value  # p2 w1 \/ m- ?3 E
}  # m# T: j9 r3 v9 n; Y: `3 H
}