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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);  : S  G' j' x: \) R, C. `
System.out.print("
; T% N! F( f/ V7 I目前共有"+count+"笔数据");
. X4 E& ]% R& f5 D; c$ pSystem.out.print("# I; A5 i4 \. c$ m) h# e3 U

/ b; c, Z7 ?, Z5 P, b2 V9 D0 s! B按任意键继续...");
# P6 s' X' y+ T  ]enter=bufin.readLine();
4 U% N( I" o* U* snew str14(htable);  ( e3 h, z  m, X/ C  x
break;  $ t. v) m' V0 `. _6 q
default:
" b5 U: D- F) ^4 a}  : o# u# v5 n6 c  m$ P; w
}
& ]* s( _) W+ m& ^2 _. B) E5 I# Q& f0 V
public int select() throws IOException//method of getting a function selector
! t5 P; D+ R" ~! {1 A' ?{
0 a, [+ @& \: O/ V4 iString input;
, }7 F5 ^# |2 s" s+ \int value=0;
2 k% q  {+ d8 ]9 B2 a8 U# Iinput=bufin.readLine();//read a input from keyboard  0 ^0 W- e4 T7 s; B" I: L
try  * o; S- e" R% F: }8 H
{  + j( x0 ^! P8 ]$ p* S
value=Integer.parseInt(input);//convert a string to a int value
% T4 \6 _, L# b}catch(NumberFormatException e)//can’t vonverted
: U/ Q& l9 H1 V/ x( |{
2 N& g1 M8 ~5 C: r" w& y( }$ mSystem.out.print("请输入选项1~6:");
3 e' Y7 w8 Z% f! W7 O0 A3 q0 v/ ?$ O, evalue=select();  ; q1 E; h; }5 J3 s/ ^, }9 W. G
}
# x! H0 h) c& t1 E. Qif(value>6||value<1)//if exceed then print a message and reenter
0 G( V/ w& T9 H3 s{  5 m; @2 \% G! o0 m
System.out.print("请输入选项1~6:");
7 u9 ^7 c; o* J# d- I2 Gvalue=select();  5 d) A) }% U  f- K+ F" p$ ~
}
8 e" k5 r8 y" B- z- k5 greturn value;//return a value
. t$ ~+ _/ t9 n7 F0 Y2 [}
! }/ a, Q# r; Z7 y$ C- ]. P' {% K: E' o
public int getid(int count)throws IOException//a method of return the number of data  & t7 j! E% W4 }! {5 J
{
# t, N+ s* a1 S! `String input;  ) G2 r+ B( g3 w/ Z- C% b7 V
int value=0;  4 p9 }) t3 M. k0 U- {7 N
input=bufin.readLine();//read a user input string from keyboard
- ?/ I3 _3 p/ n' M  w6 N1 Ttry  ( D, g0 G9 p; X6 w2 s2 C3 P3 O4 A
{
# D# z7 j: c8 W4 ^7 q; bvalue=Integer.parseInt(input);//convert the string to a int  5 M, J6 E4 [' t* p3 W8 Q* v
}catch(NumberFormatException e)//if can’t convert to a integer then reenter
' M  [4 a# V6 F4 }{  " w/ Z4 Z2 b2 r4 E& T
System.out.print("请输入数据编号:");  8 @+ D& z. f1 P/ l& J3 J
value=getid(count);  ! r. p% W% D7 c
}  ' g" A! Y; o; l% n9 I
if(value>count)//the input value is out of bound
$ y* {( [9 L* u% c" y4 b9 H+ h% Y3 q{
7 B! K2 y5 u6 B& y6 r; sSystem.out.print("无此编号的数据,请重新输入:");
8 Y# ]$ W/ C* O1 k: jgetid(count);
" K! z3 w5 s+ ~8 d6 t}  % W/ e" I  V6 N% o6 O. Y4 M
return value;//return a value  4 I" E9 m1 [1 W1 m: t
}  " ]5 R. c+ X9 y
}