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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);
" O% u3 k/ B* _4 _7 SSystem.out.print("! b( a( j( |( Z' l; X! Q- W
目前共有"+count+"笔数据");
$ U; _& C' L& A/ B+ X$ KSystem.out.print("( F5 m  K, L1 u! w5 D
, c& p- z2 A# `! C% F* x/ c
按任意键继续...");  2 i9 t2 L3 n5 S( w  }7 R4 M" E
enter=bufin.readLine();
& z1 @$ p! X9 D: Lnew str14(htable);  0 n/ Q' f; s2 o6 h# K! Z
break;  + B# q% x0 l% k+ {* r+ s' Q
default:
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4 t+ H6 p3 f" b+ Y8 s7 l8 s, W. O/ T: N
public int select() throws IOException//method of getting a function selector  5 r$ U! \) }8 j) C  C4 w
{  . L8 G7 J5 s( E) ?/ u1 z+ k3 u
String input;  0 n  [2 ~2 T, x$ K& [+ ]* D$ ~: w
int value=0;  1 j7 ~6 {  h: e, X1 \4 O
input=bufin.readLine();//read a input from keyboard
. e, {% j2 S0 O- T6 Xtry  % ~& J( C; \) h2 {* }7 [+ n3 s
{  2 K& d+ d8 i3 r
value=Integer.parseInt(input);//convert a string to a int value  ) S! [2 ~1 z: ?! s& g
}catch(NumberFormatException e)//can’t vonverted
" Y6 J* t& `, w/ Z, u8 _{  1 z& y5 i6 o) q0 t/ v8 }
System.out.print("请输入选项1~6:");
! @0 ]9 H0 W( k, C- `' k, k1 T  |value=select();
2 b. j/ w9 T& l}  ; b" t$ h# s7 M* o5 s6 d& C$ ~
if(value>6||value<1)//if exceed then print a message and reenter  % z% e9 b  u3 I" _* _9 g* o3 F
{  * f/ ~1 W1 }9 W
System.out.print("请输入选项1~6:");  9 W1 l: t& v/ ?, O
value=select();
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return value;//return a value
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6 s+ `2 Z' P9 d2 c: z: j# R2 O  i5 o* ?6 z0 D4 K
public int getid(int count)throws IOException//a method of return the number of data  4 Z2 w& b* w/ }/ b0 G. q9 |1 b3 z
{    |3 p4 R( ^/ y& P+ i  d
String input;  6 g2 w/ `( Z$ l/ F, a: Z
int value=0;  . R+ ^% Z$ d$ D$ t' S  o9 K$ e  d
input=bufin.readLine();//read a user input string from keyboard
9 B8 o2 R8 x& Z" @* Qtry  . K/ A7 g9 G7 |2 L! b
{  " k: I7 m( _' Z& B6 x* f9 f
value=Integer.parseInt(input);//convert the string to a int
+ T$ L0 d2 k' j; U% w}catch(NumberFormatException e)//if can’t convert to a integer then reenter
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System.out.print("请输入数据编号:");
0 o; R; n3 e2 a6 i6 C2 l# Fvalue=getid(count);
4 |# n. W' N2 M5 `}  0 W  T, i: f+ W6 [7 a6 f
if(value>count)//the input value is out of bound  9 Y* [5 H1 ?: j& _( a% U- t
{
% J' J0 @. O8 n# U! ?5 o. N+ }System.out.print("无此编号的数据,请重新输入:");  " @6 ^! a+ R1 I) c2 ]
getid(count);
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5 M1 }' n( A+ N$ Kreturn value;//return a value    G1 {- @3 |4 T: H8 ]  u2 `
}  , W4 H- `) o2 E$ b3 z
}