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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);
! V- M6 z5 W% I4 f1 ASystem.out.print("
, l) `: P! `3 y/ M& G& |- P目前共有"+count+"笔数据");
) _5 n9 d9 \. K* gSystem.out.print("
1 V9 \6 F* z3 |6 W" [  j( \
8 `7 `- L0 b8 I3 N: B按任意键继续...");
; E1 X! y3 c3 j$ f  [: b; Q. Genter=bufin.readLine();  6 G! Y9 E: M5 W$ M
new str14(htable);  ; L  d/ {' J& t, C. S/ O' R, {
break;
$ A) o& F) X. O& C0 P1 Cdefault:
5 P+ @% G# i6 m: G1 H9 ^}
1 J6 |4 V' i8 t4 E5 g$ e}
  O& ~$ w9 m  X8 v6 t8 s
0 E- B1 o2 Q8 p: ^1 b8 Upublic int select() throws IOException//method of getting a function selector  4 O! \. F& v! r7 B" N. b2 v
{  0 h$ }/ P* Z. A
String input;  4 j8 c* t% R9 E$ M/ }4 |
int value=0;
: v! j' a6 b6 einput=bufin.readLine();//read a input from keyboard
8 J- p) I8 D9 b' V6 Ttry
- |' q- S: Q6 d- `& C( n0 c) a{  : I* X2 \2 \: F" C& H* P8 v8 e
value=Integer.parseInt(input);//convert a string to a int value  6 O* ^( H: n6 s: R
}catch(NumberFormatException e)//can’t vonverted  " [; W' L1 s: P7 |  g
{  " U1 R4 S( h8 N
System.out.print("请输入选项1~6:");
. U6 G4 n  }; F0 ]# Z7 |+ j' y) Avalue=select();
5 _! B7 O/ }" q* I! u8 d}
% v5 u" w: |# U) w1 c' g) m7 r2 xif(value>6||value<1)//if exceed then print a message and reenter  0 {4 B: M0 p! v1 f
{
7 o% P- b" A- \5 R+ ~7 a4 T) iSystem.out.print("请输入选项1~6:");  0 `) y4 ~: i/ a' V( ]
value=select();
% G! E9 X. }2 @& D}
; j7 [! b1 F1 p0 Z- xreturn value;//return a value
8 J1 H) D4 ~0 G0 d3 p}
) @% i7 M# [9 h! ?( O0 ~7 n6 D& D- a/ b5 n+ B
public int getid(int count)throws IOException//a method of return the number of data  ! B9 ~3 t. {; E) h, E' [: P! _
{  ; w1 c9 n; v; W' A7 L& M# E
String input;
' q2 `: {2 L0 T9 l& Aint value=0;  $ o# N' }3 o/ G8 @
input=bufin.readLine();//read a user input string from keyboard  : N; J! |0 p1 b+ b& ^
try
8 [: v/ F4 s" e% l{  ) k; \) u7 G/ t, B
value=Integer.parseInt(input);//convert the string to a int  ) K, t2 @* G8 W$ i1 f
}catch(NumberFormatException e)//if can’t convert to a integer then reenter  8 x, r0 r9 d6 F0 E) ~
{
' Y+ n" A1 q5 q; @; P' x) sSystem.out.print("请输入数据编号:");
% K# h( W( X- ^$ A% x3 A! Pvalue=getid(count);
7 [3 Z! L4 g1 O* m+ a0 Q7 g. Q}  . J# n5 \2 M* X* ^; C) E6 g& u
if(value>count)//the input value is out of bound  , R- ]2 R* P, v" Q) _( _0 q5 ~
{  : |2 }9 S+ O9 K7 w8 j# L- L* K
System.out.print("无此编号的数据,请重新输入:");
9 M( O1 _3 |$ o  x, Egetid(count);
& n5 u; w0 d/ ^9 }, i6 x, e' S}  " a# B" @, {4 y) C+ p7 h$ u# `
return value;//return a value  - Y3 O/ C: Z, X  n# Y- o! x
}  0 C. i# }9 l; K" `1 U: R
}