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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);
; I! z$ @* B. X6 t8 E4 G; [# WSystem.out.print("7 Q1 _! Y3 @7 p0 |' u# A6 ^
目前共有"+count+"笔数据");  ) b/ _1 G2 B: g) ~1 F$ O: Z
System.out.print("# }) c% r3 Y  S) n

* ~9 Q- E( |+ Q9 k3 k( |6 r: l8 K按任意键继续...");
* w- r" ?+ b* _6 ]; Y/ K' henter=bufin.readLine();  8 t6 X" v( f. y2 ?# q! }
new str14(htable);  $ K' b: D, [. n- t, Q2 W7 D% o
break;  0 ~7 m# |3 Z- j" e7 W# T7 s  }
default:
3 A, X2 B  c. u& P8 g* s}
  O  m0 {5 L# L" }1 d2 I" b}  ! [" i: ^5 n# i8 c* ~  [% ~

% I* z; A( t! Mpublic int select() throws IOException//method of getting a function selector  , G# U6 D, E5 U
{
+ ~0 T5 h  w$ z9 v" Y+ r- VString input;  + l  S5 H9 Y, y3 F, i
int value=0;  : f/ ?' ?# N; k+ |4 C/ J
input=bufin.readLine();//read a input from keyboard
. p$ ~1 t) A) Ztry
/ }3 ?3 K- J% \2 N{
7 v: I& v% a" C9 y& p9 G9 rvalue=Integer.parseInt(input);//convert a string to a int value
3 p" H0 m# u4 \0 Q# g}catch(NumberFormatException e)//can’t vonverted  ; Y0 B% t# A* Z& M7 b! Q
{
" a1 _9 Z) _0 L+ P0 }System.out.print("请输入选项1~6:");  3 i2 o+ j- j$ @, V
value=select();  : ?# G. W: C* l! l
}  ( _& b/ t4 ?' A5 P
if(value>6||value<1)//if exceed then print a message and reenter
/ ^3 |0 Q7 A/ w{  * r, V9 V! Z: r/ q# e
System.out.print("请输入选项1~6:");  6 M( m( V8 P( p& Y+ D( _  l
value=select();  9 M# d: h6 F3 C5 r
}
6 G6 @8 a  p* W( w2 ~) sreturn value;//return a value
6 e( x; p( X: M$ `" l}
' H4 U0 e& J0 c# p* f' R( Y1 N2 c0 a& j& U% R' G2 }
public int getid(int count)throws IOException//a method of return the number of data  0 R" T( |# j  y8 l7 U: l
{  5 ^& u2 \1 k8 |. W/ {+ H
String input;  / P. P0 ^2 b' f# c) ?
int value=0;  ' F& s8 P, Z7 Y' Z1 d5 I; S
input=bufin.readLine();//read a user input string from keyboard  & S9 f- }! m9 l! b
try
4 ?0 f9 R1 s# \1 s; ]% T7 O{
5 d; }2 E+ ?6 Hvalue=Integer.parseInt(input);//convert the string to a int  ) b4 y: d+ v, n/ t0 @0 t" F
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  4 V- K5 G0 }; K  j
{
* j* J" L- J+ ~1 ^3 c* QSystem.out.print("请输入数据编号:");  # s# O6 T, A/ p. G9 N6 H3 N! E# j
value=getid(count);
4 }1 x# z7 S: |}  ) A' d0 {4 [! `) T" |
if(value>count)//the input value is out of bound
) j- p/ i) M& G, T& J4 N* t{
: M" I+ ~. K3 n* @* WSystem.out.print("无此编号的数据,请重新输入:");
3 a. B/ n- ?1 {0 E# sgetid(count);
/ U5 y. Q% N1 ?. i}  8 j; T5 A6 d8 r' X
return value;//return a value
0 d- q. m+ N3 G% U7 y& o}  $ ?4 ?% u( ~2 \8 g
}