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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);
9 N; {# f9 ?6 i  z0 ~, NSystem.out.print("
: W: O' U9 A. h: A目前共有"+count+"笔数据");  9 l2 e. V7 z% i: ~2 ^
System.out.print("
  [% p* n6 F8 a7 S4 {) n. k8 v8 y# b0 a* M( n
按任意键继续...");
  g: t1 O7 Y3 B& t. Oenter=bufin.readLine();    d' b5 c# I+ K+ C( a+ C
new str14(htable);  ' P$ K( y4 {6 q8 i
break;
1 g5 K, ]+ D, D* v; xdefault:  0 Y0 a( S7 g) [( X$ M3 M6 U
}  ; `% e( l1 T. ~8 a
}
5 e: u9 x: R, _/ [1 w6 z" u) `5 @+ a5 _, g+ v4 V. }
public int select() throws IOException//method of getting a function selector
# t7 {5 a: V6 I: t1 T$ P{    p( y. |6 z  b5 h0 ^4 ^
String input;
5 U2 }/ f1 l  T* `1 V# ?, Nint value=0;  3 \5 p0 q! T" j: b/ ~9 p# K
input=bufin.readLine();//read a input from keyboard
3 n: y$ d& \: f% ttry
9 s6 n4 V8 ?5 g7 m{  + Y# L: O  N. g3 |8 S
value=Integer.parseInt(input);//convert a string to a int value
1 T/ r2 a1 m0 D}catch(NumberFormatException e)//can’t vonverted
8 {, W; x# N9 B# D{  ) b) M' O% k+ u5 B. V# e, V
System.out.print("请输入选项1~6:");  ! G4 a$ C& u$ n4 h) l' K  n/ m
value=select();  ! K# _" p. u* [, Z6 f
}
# i" @, v7 I5 [% @if(value>6||value<1)//if exceed then print a message and reenter  ; @' b7 U$ e/ _0 v
{  0 C3 B: F' D. X7 Y2 X: d! r
System.out.print("请输入选项1~6:");
7 q& e* h9 @* a- s0 y3 y2 g7 ^! hvalue=select();  . s& [2 W. [: ~* `* |1 Q: q2 F
}  ( Q5 D6 J! R3 M) s8 ~, g; q
return value;//return a value  , [. P2 ~3 _- o
}  ! o! k# Z0 [( f. [/ [
3 Z+ B8 l+ ~& b7 f6 g; {- C
public int getid(int count)throws IOException//a method of return the number of data  2 s) a& o6 f. q$ }7 ~" s( W! M
{  - I: l0 t/ B" p1 n, w% `- o! o% J
String input;
' t& @- Y' x( `- o3 i6 r* v6 j' aint value=0;
7 C: P0 b+ [  einput=bufin.readLine();//read a user input string from keyboard
# D" m$ i( g9 |: O# y7 [try
! G% E7 q; n; J" _{
" e: N( w2 V) ?0 F0 Ovalue=Integer.parseInt(input);//convert the string to a int
  @, W$ j+ B8 x1 @. V}catch(NumberFormatException e)//if can’t convert to a integer then reenter
( s/ G" ?- z* J" @{
# z2 c) g2 r) QSystem.out.print("请输入数据编号:");
. E" \% u% B3 S2 x! Svalue=getid(count);
% l  @5 L) u- y" w, g2 S}
5 t# F2 l# ~3 u! M  C+ lif(value>count)//the input value is out of bound  / O$ O2 ?% N6 `
{
3 W8 m# Y3 X2 |  J- FSystem.out.print("无此编号的数据,请重新输入:");  % W7 G( s+ f7 E. W
getid(count);  # N0 d- x1 B' d9 f$ c: }4 }7 m% g
}
6 U- \  q$ A) J  breturn value;//return a value
, t. ~( S4 R, d% Y0 `}  # x0 m6 K7 J' c# g6 z
}