小编Dil*_*lis的帖子

我有3节课.这似乎是基本问题.但我无法通过谷歌搜索找到答案.

public abstract class Test {

    void t1()
    {
        System.out.println("super");

    }

}
 public class concret extends Test{

    void t1()
    {
        System.out.println("child");

    }
    void t2()
    {
        System.out.println("child2");

    }

}

public class run {
    public static void main(String[] args) {
        Test t=new concret();

        t.t1();
    }

}

如何调用抽象类t1方法？由于我无法从抽象类创建对象,如何在抽象类中调用t1？谢谢.

我使用预处理语句编写了select语句.每次尝试运行它都会出现此错误.我怎么过来这个错误？我的jdbc连接器是mysql-connector-java-5.1.13-bin.jar.我的代码:

 public Main_add_ad_to getAdDetail(int ad_id) {
    Dbconnection db = new Dbconnection();
    Connection con = db.getConnection();
    ResultSet rs = null;

    PreparedStatement stmt = null;
    Main_add_ad_to detail_to = new Main_add_ad_to();
    try {
    String selectSQL = "SELECT *  FROM ads_tbl where id = ?";

    stmt = con.prepareStatement(selectSQL);
    stmt.setInt(1, ad_id);
    rs = stmt.executeQuery(selectSQL);
    while (rs.next()) {

        detail_to.setCat_ad(rs.getString("cat"));
        detail_to.setType_ad(rs.getString("sale_type"));
        detail_to.setBrand(rs.getString("brand"));
    }catch (SQLException ex) {
        Logger.getLogger(Lands_cls.class.getName()).log(Level.SEVERE, null, ex);
    }
return detail_to;
}

错误代码..

2013年10月1日下午1:23:23 sanin.lands.model.View_ads_cls getAdDetail

SEVERE: null
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL …