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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);
& f! {+ a0 }+ ESystem.out.print("
% Z$ \6 i; p% ~  u目前共有"+count+"笔数据");
- L- x# T% ~7 eSystem.out.print("
/ w0 z: m1 }7 v- a3 I3 O
3 }* z: X3 O* q% c按任意键继续...");
6 W4 l! U2 h8 R9 r  benter=bufin.readLine();  3 b0 C8 c+ g# N' {
new str14(htable);
2 {) P2 Y3 }0 _2 [2 N) ybreak;
. y" n) s3 v; v) e: Wdefault:  # i& [) K0 k9 D! o: q8 \$ ?* @
}  % ~; A* @+ b5 D* @: T8 w. R
}  , U2 Z# Z9 p% a8 l  I

# h2 x0 z# I) U) r6 Z5 Spublic int select() throws IOException//method of getting a function selector  2 K! }" V$ ?5 H: V" R! _0 l- B
{    b5 v; D; N/ Q! x. ?9 h1 \
String input;
3 e4 ^$ |9 z2 P6 ^int value=0;  * f/ l- u8 L) a( D0 m5 l4 @8 _
input=bufin.readLine();//read a input from keyboard  * P& R1 o# M$ h. r' P2 ]
try  # X. ]# m- M5 w" Z
{
0 |* o. u1 v5 }8 W3 ?9 {value=Integer.parseInt(input);//convert a string to a int value
  t6 F# o) h0 X}catch(NumberFormatException e)//can’t vonverted
9 H. i7 |) O0 y6 n7 j{  ! W4 \  T# f1 M+ I
System.out.print("请输入选项1~6:");
+ X* L8 K( ~1 G) J( c6 K5 Evalue=select();  % I0 D9 j$ F4 f' N
}
: m5 }$ N: S' J2 H0 H3 A/ T9 mif(value>6||value<1)//if exceed then print a message and reenter  8 ~$ E5 e8 m, Z3 @( a* \0 C! Z
{  ) q! l0 I$ ~8 l( r5 z
System.out.print("请输入选项1~6:");
5 V+ G" H) J& }value=select();  6 I4 B9 H6 I* g" U- z* Q
}  ! q7 N5 u; G0 L2 K1 |
return value;//return a value
, |2 I, x$ a- p2 F8 h' `6 s( m9 p}  % ^" i/ B4 Q3 O3 e, y

; E' n( a4 {5 tpublic int getid(int count)throws IOException//a method of return the number of data
9 Y& j" s5 V/ L" V{    s7 \& Y- K1 k) O& P: `; m/ e
String input;
4 p$ V7 y0 ]( k! ]3 k$ A$ f3 @int value=0;  % i) b  a0 E! x
input=bufin.readLine();//read a user input string from keyboard
; H% z: t) h) [' v1 Vtry  : p$ H7 I4 {" ]2 c' v
{
! j" {# ]. I1 Rvalue=Integer.parseInt(input);//convert the string to a int  8 E6 E  [3 G* G( T6 g4 f
}catch(NumberFormatException e)//if can’t convert to a integer then reenter
2 _6 l4 z# y  v( X- X. x{
5 _5 F6 b0 p. q8 _6 S- I( XSystem.out.print("请输入数据编号:");  . \) f$ o2 @9 c7 R# y# B
value=getid(count);
4 ]6 h9 U, u! t7 n7 _- t* D" u- V}  ) q6 f: g2 x6 F$ L" u
if(value>count)//the input value is out of bound
/ u8 R# T8 n+ f- P& R{  / i; k+ G4 K  Y) s: d1 e' J0 R
System.out.print("无此编号的数据,请重新输入:");  # y. D& K2 ~* f. v
getid(count);  0 q: [7 j: A9 a4 A  h/ l
}  7 v& P6 |- v/ b. V+ I
return value;//return a value
, Y2 s6 K* P; @8 y}  ) n; L7 \' K7 s9 j. S+ @0 }) ?0 y. J
}