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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);  " r7 i  ]9 v$ ^8 \/ i' E- b
System.out.print("7 p# ^/ y- x4 W- M% v2 e
目前共有"+count+"笔数据");  - L6 y( ~$ }5 y7 s
System.out.print("+ R' P. N4 V2 r5 e2 a
$ R. e: J# y; w; H2 T
按任意键继续...");  - F; n' V7 d# t
enter=bufin.readLine();  6 a$ A9 s: G& t1 D) U7 y
new str14(htable);  9 j3 U+ f2 w5 h4 R0 k( T
break;  & N" R; W9 G5 z* S
default:
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7 \5 ?  p/ m# epublic int select() throws IOException//method of getting a function selector
& |6 r' D( t$ e9 c4 \8 e' `# h0 G{
$ W0 }: E0 ^2 }' [, a& sString input;
+ M( K' H. v# Q( Eint value=0;  " w0 ?1 n2 Z  r/ _% C. D
input=bufin.readLine();//read a input from keyboard
3 T6 k# z5 A6 z" q# _- Ntry  ; z# C! _1 X/ B9 Y3 d0 h, n6 w" h
{  # N& p/ I+ ^! I. r$ A; g
value=Integer.parseInt(input);//convert a string to a int value
# N- y1 h, F+ M0 U: f}catch(NumberFormatException e)//can’t vonverted
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System.out.print("请输入选项1~6:");
" @' z. ?1 U: n9 e0 Yvalue=select();
5 y1 l* v" P" D0 D  D* b0 v}
" [) e! K- R3 L& U$ xif(value>6||value<1)//if exceed then print a message and reenter
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System.out.print("请输入选项1~6:");
- m/ p" b5 K, |' d  E* Rvalue=select();  6 \, d& e/ [. X1 ?" t
}
- M: f& Y6 _" S6 D5 p, E. m! vreturn value;//return a value
1 o) J$ {2 i: V# {}  ! Q, q* S+ a& m1 e, q, ?
7 [, t, _; a) ^  \, S$ w
public int getid(int count)throws IOException//a method of return the number of data
8 E, W7 t+ i8 s2 m/ y9 w  ~{
" x1 k  h! F) l  ^. H/ KString input;  4 B& g5 i# N9 W. P8 S* E" Y
int value=0;
1 N  ~# q9 q& ?! W% Hinput=bufin.readLine();//read a user input string from keyboard
* G" O6 j9 O9 m. }7 otry
" [6 |5 G( o1 q0 q# C{
/ W; P" b8 ~3 r* R  _' pvalue=Integer.parseInt(input);//convert the string to a int  0 f) b, ?# B  q+ X1 }
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  3 T. l) O1 ]  f
{  6 Y' I! }+ F- V+ h
System.out.print("请输入数据编号:");
+ e% e3 S- A1 p! ivalue=getid(count);  $ |6 @5 t/ H2 @2 V: x+ f
}
- l/ K" ~) d$ g0 q. N3 U1 ?if(value>count)//the input value is out of bound
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1 }: w4 A  b* P1 F$ X& J  V9 c( nSystem.out.print("无此编号的数据,请重新输入:");
! Q  L4 \% T! j8 z& n0 b; Agetid(count);
! b) z) W- q0 I  O}  0 y) d, B. d* a4 Y" H
return value;//return a value  % S# g" i6 ~+ R: d; t
}
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