小编Gen*_*kin的帖子

所以我有一个MySQL JDBC驱动程序的.jar文件,它位于我的库源文件夹下,我有以下代码:

public static Connection getConnection() throws SQLException {
        Connection conn = null;
        try{
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            String url = "jdbc:mysql://50.56.81.42:3306/GUEST_BOOK";
            String user = "user";
            String password = "pass";

            conn = (Connection) DriverManager.getConnection(url, user, password);
        }catch(ClassNotFoundException e){
            e.printStackTrace();
        }catch(InstantiationException e){
            e.printStackTrace();
        }catch(IllegalAccessException e){
            e.printStackTrace();
        }
            return conn;

    }

但是,它总是给我这个错误:

INFO: Server startup in 645 ms
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1678)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1523)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:169)
    at gbook.DbHelper.getConnection(DbHelper.java:14)
    at gbook.DbHelper.getGuestBook(DbHelper.java:51)
    at org.apache.jsp.index_jsp._jspService(index_jsp.java:83)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:433)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:389)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333) …

我是Fedora 17和Emacs的新手,无法弄清楚如何告诉我的emacs使用最新版本的python.

我找到了一些信息,我应该更改python-python-command变量或显示新解释器的路径,怎么做？

我想知道如何使用指定字符和长度的java生成所有单词

String first[]={"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};
String second[]={"a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"};
String ch ="";  
String total[];

for(int i = 0;i<26;i++) {
    for(int j = 0;j<26;j++) {
        ch+=first[i]+first[j];
        System.out.println(ch);
    }
}

我只得到这个程序只有576个单词,但26个单词!单词是4.03291461×10 ^ 26

如何在java中编写程序？