java - 无法从 java.sql.Statement 转换为 DataBaseConnection.Statement

Question

我有这个问题，eclipse 的快速修复建议我为这一行的语句添加一个强制转换:

state=conex.createStatement();

和此行的另一个声明:

result= state.executeQuery("SELECT * FROM itshop.products");

在输出中我没有收到任何东西，当我进行转换时错误消失了，但是我没有任何输出。你能检查我是否正确连接到我的 mysql 数据库吗？

代码:

import java.sql.*;

public class Statement {

      public static void main(String[] args) {
          Connection conex=null;
          Statement state=null;
          ResultSet result=null;
          try
          {
              Class.forName("com.mysql.jdbc.Driver");
              conex=DriverManager.getConnection("jdbc:mysql://localhost:3306/itshop","user","pass");
          }
          catch(Exception e){
              e.printStackTrace();
          }
          try
          {
              System.out.println();
              state=conex.createStatement();
              result= state.executeQuery("SELECT * FROM itshop.products");
              result.next();
              int RowCount=result.getRow();
              System.out.println("Rows Number Are:"+RowCount);
          }
          catch(Exception e){
              e.printStackTrace();
          }

      }
}

当我没有为上面的行进行转换时显示错误:

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
    Type mismatch: cannot convert from java.sql.Statement to      DataBaseConnection.Statement
    The method executeQuery(String) is undefined for the type Statement

    at DataBaseConnection.Statement.main(Statement.java:22)

Answer 1

问题是您的类(class)名称。有两个Statement类:

1. java.sql.语句
2. DataBaseConnection.Statement

尝试将状态变量声明为 java.sql.Statement 类型:

public class Statement {

      public static void main(String[] args) {
          Connection conex=null;
          java.sql.Statement state=null;
          ResultSet result=null;
          ....
          ....
      }
}    

否则将您的类重命名为 Statement 以外的名称