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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);  - m6 O7 a% T9 h: E, C
System.out.print("
0 R: D; l- _1 N9 `& N# X3 N) P目前共有"+count+"笔数据");  $ b, v8 i6 b6 `/ a8 `# Z% C
System.out.print("
- O4 _! u  B% D3 A! G" I+ a( A8 H: Z3 q: c
按任意键继续...");
# G7 n4 r  D; R. d8 {! Z4 p7 {enter=bufin.readLine();
8 {' ]% h: f- n8 Nnew str14(htable);
) U% k4 l$ k' v4 [break;
/ e* v5 u/ v- `4 t  `) H3 Kdefault:  ) O' |6 |+ W. T
}
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public int select() throws IOException//method of getting a function selector
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String input;
& m7 m+ Q) i0 P/ p" O. p! hint value=0;  3 H+ J: X2 j- F3 v3 q
input=bufin.readLine();//read a input from keyboard    @& O2 x8 m/ |# Z$ p5 B( b1 ^; p. u
try
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value=Integer.parseInt(input);//convert a string to a int value  / ?$ e* r: |- j% o
}catch(NumberFormatException e)//can’t vonverted
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System.out.print("请输入选项1~6:");
- I; q% B2 }# @/ {5 c6 svalue=select();
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! o7 ]) `2 {: E& _if(value>6||value<1)//if exceed then print a message and reenter
! |- R! r1 T8 R0 Y3 h5 Q5 y" H{
; l$ f; |1 A& s2 }$ N' Y3 S# kSystem.out.print("请输入选项1~6:");
( `0 k: E# |9 s7 l0 N  lvalue=select();
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return value;//return a value  8 g' G5 i5 z! u4 R/ r- p
}  % r/ R4 i, e- g+ }! |3 F. W
$ \: e2 w0 T5 z7 J0 R* p
public int getid(int count)throws IOException//a method of return the number of data  ( ]" ]& ?6 e* v5 h$ D4 `
{
1 p- q' ~! r4 y$ s0 e2 gString input;  - P- S9 I* O* \& i9 A) ^
int value=0;  ( v4 ~* v* G( e! C$ y
input=bufin.readLine();//read a user input string from keyboard  ; C9 u# ?3 W+ u$ M3 ^. Q
try  ) k6 b( T. O# P
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value=Integer.parseInt(input);//convert the string to a int
; j& F" \$ ]" V( ?- v% B7 R}catch(NumberFormatException e)//if can’t convert to a integer then reenter  1 n) Y" B; W# T' ?" Y- z$ S- N
{  3 v; h: j9 F3 ~! C& {
System.out.print("请输入数据编号:");
# d4 V# i) ^( o' y# A+ X6 n. gvalue=getid(count);
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if(value>count)//the input value is out of bound  ! w  A: _0 Y& \
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System.out.print("无此编号的数据,请重新输入:");
5 K. ?& W( F* W& T& m0 B' B5 }# `4 ~getid(count);
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return value;//return a value  ' i( j  O/ t# L$ z( `% h; U7 t
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}