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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);
$ ]$ y1 i1 i4 R( R; d/ NSystem.out.print("
- }8 }% R: A$ ~3 h3 ]目前共有"+count+"笔数据");  1 @# _; c! @" c/ c# u( c
System.out.print("; `9 `( X# ?; g9 `' ^

/ P, Q- T% O4 ~: T$ t- ]. @- ^按任意键继续...");    {' B- a2 k9 ^( k& ~  }
enter=bufin.readLine();  8 v% V& z: N3 n+ N! L4 t  r
new str14(htable);  - d% ]( b0 _- G/ m# @
break;  & R- |0 v; g" ^4 z; L
default:  ; ^! v9 Y4 p) z9 s, F' W( \3 \( N
}
) z! B; V; e4 X6 W}  " ?3 G( o5 Q0 }+ o1 C

2 m5 X" C! U( v! w- Ppublic int select() throws IOException//method of getting a function selector  8 @9 V3 Z: ?" K* q' T, `/ x
{  & ?- O8 l5 q% E" X$ G% j
String input;
; S& {/ m$ S/ Q' e; dint value=0;
( k4 D$ H. m5 N6 d3 dinput=bufin.readLine();//read a input from keyboard  4 I- ^6 Z' j1 g$ v: R; f) N
try
. U8 m1 h5 H1 y  j* o{  9 {0 f' L, b: W' ]3 ^6 e  r3 g/ Y
value=Integer.parseInt(input);//convert a string to a int value    _: p0 C9 ^" o, U# @0 I( D
}catch(NumberFormatException e)//can’t vonverted
, i% f6 ^; U& X{
6 S& |, I$ P; aSystem.out.print("请输入选项1~6:");
2 V+ X$ L! V& y" wvalue=select();  9 ^6 H9 f0 \: ?5 s: i
}  ' t! I" I+ z$ s
if(value>6||value<1)//if exceed then print a message and reenter
' C9 i# L. P0 Q* U" ?{  2 Q1 N2 Q2 ?: ^3 H+ p7 k" z* R
System.out.print("请输入选项1~6:");
0 s: F. G* Z! avalue=select();  9 K' v# e+ g1 N* H- O3 _
}
/ I  N8 R1 @' @5 Q% E% v7 wreturn value;//return a value
1 f9 {8 H+ Z1 h6 c6 c5 W& G6 j+ u}
1 F+ h/ c, ^1 x7 u: p/ D2 z6 V) J4 _, b, c' R) T& p
public int getid(int count)throws IOException//a method of return the number of data  5 Z8 |+ S8 X- T4 ^1 ?
{  $ T' ]" T; J) k) g
String input;  ( L) a/ p- s3 E( y5 q! Z  k
int value=0;
# e5 Z' @& V; O: j2 b; e& rinput=bufin.readLine();//read a user input string from keyboard
/ i# t: `4 A9 gtry  ) c% V, `1 o/ R( \8 K; x
{
& _  y: d; t/ }( M1 rvalue=Integer.parseInt(input);//convert the string to a int  / p4 h9 ^& o% W. k5 J  t) D
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  % Y. A+ d9 j, D2 w7 T
{  9 w$ e3 U0 `8 g# y# }! H, I
System.out.print("请输入数据编号:");  / H  s% b5 e! N8 l" M) l: e& J2 W% {
value=getid(count);  6 W! A, ?& O' @! v, S" N4 x
}
! L  v: ~& J$ S( z8 x1 Uif(value>count)//the input value is out of bound  7 M# d- }4 W- S& @0 ~8 a1 s. L% T
{  ! Z8 o$ ~: t% I: r3 s
System.out.print("无此编号的数据,请重新输入:");
: l2 D/ i9 E6 Qgetid(count);  5 z  n8 x$ N- Y' j
}
( v  E% X0 b* ?- C  Hreturn value;//return a value  : t- S, C8 S9 k
}    {$ s+ c/ Z5 B) l& C' Z
}