[Java]代码    

import java.sql.DriverManager;  import java.sql.Connection;  import java.sql.SQLException;  import java.sql.ResultSet;  import java.sql.Statement;    public class PG{   public static void main(String []args){    System.out.println("PostgreSQL JDBC...");    try {     Class.forName("org.postgresql.Driver");    }catch (ClassNotFoundException e){     System.out.println("could not find postgreSQL JDBC Driver");     e.printStackTrace();     return;    }    Connection connection = null;    try {     connection = DriverManager.getConnection(       "jdbc:postgresql://localhost:5432/postgres",        "postgres",       "");    }catch (SQLException e){     System.out.println("Connection Failed");     e.printStackTrace();     return;    }      if (connection != null){     System.out.println("connect db successful!");    }else {     System.out.println("Failed to make conn!");    }    try {     Statement  stmt = connection.createStatement();     ResultSet rs = stmt.executeQuery("SELECT 1 AS A");     if(rs!=null){      rs.next();      System.out.println(rs.getInt("a"));     }else {      System.out.println("null");     }     rs.close();     stmt.close();     connection.close();    }catch (Exception exp){     exp.printStackTrace();    }   }  }