Hashtable简易数据库程序

王朝other·作者佚名  2008-05-31
窄屏简体版  字體: |||超大  

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[i]+" "+sortdata[i]);

System.out.print("

目前共有"+count+"笔数据");

System.out.print("

按任意键继续...");

enter=bufin.readLine();

new str14(htable);

break;

default:

}

}

public int select() throws IOException//method of getting a function selector

{

String input;

int value=0;

input=bufin.readLine();//read a input from keyboard

try

{

value=Integer.parseInt(input);//convert a string to a int value

}catch(NumberFormatException e)//can’t vonverted

{

System.out.print("请输入选项1~6:");

value=select();

}

if(value>6value<1)//if exceed then print a message and reenter

{

System.out.print("请输入选项1~6:");

value=select();

}

return value;//return a value

}

public int getid(int count)throws IOException//a method of return the number of data

{

String input;

int value=0;

input=bufin.readLine();//read a user input string from keyboard

try

{

value=Integer.parseInt(input);//convert the string to a int

}catch(NumberFormatException e)//if can’t convert to a integer then reenter

{

System.out.print("请输入数据编号:");

value=getid(count);

}

if(value>count)//the input value is out of bound

{

System.out.print("无此编号的数据,请重新输入:");

getid(count);

}

return value;//return a value

}

}

 
 
 
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