Coding study: December 2014

Tuesday, December 23, 2014

简单jsp教程--使用jdbc连接数据库

备注：jdbc是用来连接tomcat和mysql的，需要下载connector

1、首先在MySQL数据库中建立books数据库，再建book表。
然后插入数据。SQL语言如下：

create database books;

use books;
create table book(bookId varchar(50),bookName varchar(50),publisher varchar(100),price float,constraint pk_book primary key(bookId))

insert into book values('1001','An inconvenient truth','电子工业出版社',45.00);
insert into book values('1002','The satanic gases','电子工业出版社',49.00);
insert into book values('1003','Global climate change and wildlife','电子工业出版社',59.00);
insert into book values('1004','Environmental resource handbook','电子工业出版社',59.00);
insert into book values('1005','American heritage science dictionary','电子工业出版社',56.00);

2.新建sql.jsp
<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*"%>
<html>
<body>
以下是从MySQL数据库读取的数据：<hr>
<table border=0>
<tr><td>ID</td><td>书名</td><td>出版社</td><td>价格</td></tr>

<%
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection con=java.sql.DriverManager.getConnection("jdbc:mysql://192.168.1.8/books?

useUnicode=true&characterEncoding=GBK","root","1234");
Statement stmt=con.createStatement();
ResultSet rst=stmt.executeQuery("select * from book");
while(rst.next())
{
out.println("<tr>");
out.println("<td>"+rst.getString("bookId")+"</td>");
out.println("<td>"+rst.getString("bookName")+"</td>");
out.println("<td>"+rst.getString("publisher")+"</td>");
out.println("<td>"+rst.getFloat("price")+"</td>");
out.println("</tr>");
}
//关闭连接、释放资源
rst.close();
stmt.close();
con.close();
%>
</table>
</body>
</html>

we can get

以下是从MySQL数据库读取的数据：

ID	书名	出版社	价格
1001	An inconvenient truth	Bogdonoff & Rubin	45.0
1002	The satanic gases	Rodale	49.0
1003	Global climate change and wildlife	Cato Institute	59.0
1004	Environmental resource handbook	Wildlife Society	59.0
1005	American heritage science dictionary	Houghton Mifflin Book	56.0

Sunday, December 21, 2014

快速排序实现

注：此快速排序取第一个值为pivot，把小于pivot的数放到左边，大于的放到右边

public class QuickSort {

public static void main(String[] args) {
int arr[]=new int[50];
for(int i=0;i<arr.length;i++)
arr[i]=(int)(Math.random()*100);
//int arr[]={ 49, 42, 36};
//..int arr[]={8,7,8,8};
//for(int i=0;i<arr.length;i++){
// System.out.print(arr[i]+" ");
//}
System.out.println();
quickSort(arr,0,arr.length-1);
for(int i=0;i<arr.length;i++){
System.out.print(arr[i]+", ");
}

}
public static void quickSort(int[] array,int start,int end){
int temp;

if(start>=end){return;}//大于号非常重要，如果没有，会导致index越界
if(start==end-1){ //base condition，两个数的比较，必须有
if(array[start]>array[end]){
temp=array[start];
array[start]=array[end];
array[end]=temp;
return;
}else
return;
}
int pivot=array[start];

int i=start+1;
int j=end;
while(i<j){
while(array[i]<=pivot&i!=end){//注意=很重要，否则无限循环
i++;
if(i==end&array[i]<pivot){
//非常重要，这是极端情况，考虑到如果pivot取的是最大值的情况
array[start]=array[end];
array[end]=pivot;
quickSort(array, start, i-1 );
return;
}
}
while(array[j]>=pivot&j!=start){
j--;
}
temp=array[j];
//i,j交换后需要交换回来，例如8(start),0,3,16(j),5(i),18,12,9 i=4,j=3
array[j]=array[i];
array[i]=temp;

}
temp=array[j];
array[start]=array[i];
array[j]=pivot;
array[i]=temp;
//System.out.println("j="+j+" start="+start);
quickSort(array, start, j-1 );
quickSort(array,j+1,end);

}
}

0, 1, 1, 2, 2, 3, 4, 15, 16, 17, 19, 22, 25, 27, 30, 36, 40, 41, 46, 46, 51, 53, 55, 55, 58, 59, 63, 64, 64, 65, 66, 66, 72, 73, 73, 74, 77, 78, 78, 78, 81, 81, 81, 86, 91, 92, 95, 99, 99, 99,