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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);
' y; k  Q; a# B; `# J4 h0 ?System.out.print("( b$ r6 L. i" q
目前共有"+count+"笔数据");
$ U( [2 f2 K+ H- dSystem.out.print("
, H  C8 M. K# d; M; U  h' N: i% p/ W" Z
按任意键继续...");
" z/ b/ Y/ p; y2 q9 F% Uenter=bufin.readLine();
+ ^( s4 B# Z1 l( C/ h7 s" unew str14(htable);  8 M6 j# a% M. L& S  y- a$ r
break;
" z* W: C! X. X+ i# `9 Q1 Vdefault:
1 ]9 v% ]. }& K0 r! M; r3 e}
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public int select() throws IOException//method of getting a function selector
  S7 \# |! S4 N9 U{  1 J9 ^+ j' Y9 V5 K
String input;
- x* |( v3 D" j; p; F# V* w& tint value=0;  0 D* a) Z! t- U  j- I  X
input=bufin.readLine();//read a input from keyboard
+ u; j: Y8 j3 q! b0 ntry
2 `/ [5 G+ B% n; p{  ' U; d, w0 {! L* E( c( \
value=Integer.parseInt(input);//convert a string to a int value  8 {" \9 B2 ?* w2 m; s2 G, U1 o8 j
}catch(NumberFormatException e)//can’t vonverted
/ Q% e7 M  K/ _{
. U* Y" Q5 i$ H2 p% LSystem.out.print("请输入选项1~6:");  0 [& I& ^; p8 H: Z7 b# G+ @
value=select();  3 v% y4 K6 l; H; B/ P4 ^, P2 l
}
" [5 a$ K0 w' n; F& Z: L: g" W* ?* Xif(value>6||value<1)//if exceed then print a message and reenter  / |- w0 |) P/ f5 h9 ~  p
{
/ J3 R- F& ^# X/ n; n1 ^7 K" E6 H* o4 NSystem.out.print("请输入选项1~6:");  4 o, X' v; x8 D
value=select();    r- c  S5 _& [6 P
}  . I7 E, J+ u3 n+ e
return value;//return a value
& a. T6 ]2 O) |/ r3 n1 q1 X6 }}
: ]) |; J7 Z( q2 z5 u- g, N6 V2 |
. ~9 d9 j. ~/ `, kpublic int getid(int count)throws IOException//a method of return the number of data  * [3 q' W. N8 D  a0 R- b
{  7 I  z8 V8 A; @( e1 n) x* ^/ O/ f& e# C
String input;
& a4 n. P! O" ]  D& kint value=0;  ' `! a& j& t# e( ~+ V
input=bufin.readLine();//read a user input string from keyboard  7 ^; N1 h' i+ [5 K3 L; t
try  2 E  B, `" y; [& f, F7 y
{  5 O, o5 n6 J( f& X
value=Integer.parseInt(input);//convert the string to a int
2 G3 A/ u8 |, ^$ o9 Y  N}catch(NumberFormatException e)//if can’t convert to a integer then reenter    X% q* b3 x* d' f) f
{
! u" {9 B/ ~+ m( L4 kSystem.out.print("请输入数据编号:");
' w1 O0 L4 Y% L% lvalue=getid(count);  6 R7 [0 O" Q: L/ V5 t4 x
}
/ L( F: F& ]1 L5 T. nif(value>count)//the input value is out of bound
# b5 s% q$ Y" t& D: G( F  K- R{  ; d+ @5 m3 i# M, M. [4 \
System.out.print("无此编号的数据,请重新输入:");
2 A( P  q6 P! Q, W8 S4 l! hgetid(count);
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return value;//return a value
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