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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);
  g" ]/ M0 |; v8 C9 j6 g/ PSystem.out.print(", w! t5 H/ g4 S2 t( d) ]
目前共有"+count+"笔数据");  ' Z0 ]2 N( p- C$ X8 S8 ]' {; \( i( `
System.out.print("
5 ]6 ^% K- Z, J) ~/ t, W
* u% E  O% M/ [( }7 E' l按任意键继续...");  ; y0 n7 }) w/ ]/ ^
enter=bufin.readLine();  ' M$ G& z4 a' V: e) f# q" c# A
new str14(htable);
! {/ }$ b$ j, G2 jbreak;  . T0 y  t, B( Y) D! g$ E% }- E$ m0 m
default:
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) W+ T/ E0 X+ w
5 B' I/ b5 b' tpublic int select() throws IOException//method of getting a function selector
. O$ S. d/ l- x4 t) q{
, D) A7 ^. M6 Z/ T9 o+ M5 NString input;
; k7 Z: @2 U2 b3 gint value=0;  ) j7 v3 x2 L: Y+ ]2 e9 H) \% o
input=bufin.readLine();//read a input from keyboard
( ]$ p0 S! A: z6 qtry  1 e4 f! q- l2 ?$ W- v. Z
{  6 I/ X! e- x9 ]9 Y4 M/ Z& J0 C
value=Integer.parseInt(input);//convert a string to a int value  / p/ N! Z6 e. [
}catch(NumberFormatException e)//can’t vonverted  # t9 ?) ^, X9 a$ z
{  * v/ M6 k9 T4 k3 ]% O% c* J
System.out.print("请输入选项1~6:");  9 R. n! l1 S! P. ^: E9 F
value=select();
* e: F3 j2 i- D* U" Z}  0 s1 t! p, f/ ^6 U# s% q
if(value>6||value<1)//if exceed then print a message and reenter    \$ C% S. Q4 \6 Y4 W+ z3 r
{  7 p. C) Y0 }$ f# A6 j* O! p8 o! ^
System.out.print("请输入选项1~6:");  ! ?8 x) p9 W- N% }6 p0 c1 t" ?- }
value=select();
# s  p% E- F) P4 C, \9 R}  . u) I: }2 [; O/ ?' g. W
return value;//return a value
/ N8 o! G0 J. B; \+ V' ]}
( O% e; ]" \6 _
5 B* \3 A4 m% n, e& B  N6 u3 ppublic int getid(int count)throws IOException//a method of return the number of data  0 d; G  i3 m" F
{
8 o' d1 d) X& e0 [/ UString input;  ( @. k% K7 I! r' G3 r+ M. B
int value=0;  0 q1 A# V6 |% b% `6 A8 _$ H8 H
input=bufin.readLine();//read a user input string from keyboard  6 w6 t" Y; ?, Y' @& r; g, `
try
# [( X/ i( L: t" B; M" U{  7 ^' `  I6 v3 y0 z; z
value=Integer.parseInt(input);//convert the string to a int  ; n, J1 P/ w$ t1 R, y! B  [
}catch(NumberFormatException e)//if can’t convert to a integer then reenter
/ [, |' a- J& \9 G7 A9 f{
/ G0 v* R6 d9 p5 U( ]System.out.print("请输入数据编号:");  2 x, W- @5 M8 E. a. H0 G( C
value=getid(count);    v. V- S  |7 Q" u: @# b
}
& B( y0 W: ~0 ^* \; Mif(value>count)//the input value is out of bound  7 t6 a6 d8 @, d' m2 C) y
{  $ I, V8 U1 [2 g( s  o; d% [/ `% _
System.out.print("无此编号的数据,请重新输入:");
# y9 E1 P0 Q7 f' l9 [getid(count);  ' B) m/ A9 f2 q$ k; C% N  i% E7 i: D
}
return value;//return a value
; {$ i2 ^0 m8 [" W}  0 X: y) u! b1 ~, }% |: q- c
}