麻烦大神们看看这代码哪里错了，怎么改？
照书上打的一个java DB的数据库访问工具类，但出错了,private static InitDB initDB_obj = null;和 if(initDB_obj==null)
initDB_obj = new InitDB();
return initDB_obj;这两处都报错了，为啥错了，咋改呀？是因为initDB_obj是一个文件还是什么别的吗？
/*
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*/
package used_car;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
private static InitDB initDB_obj = null;
/**
*
* @author Mechrevo
*/
public class InitDB {
private String DBDriver = null;
private String url = null;
private String user = null;
private String password = null;
private Connection conn = null;
private Statement stmt = null;
private ResultSet rs = null;
public InitDB(){//Java DB网络模式的访问
this.DBDriver = "org.apache.derby.jdbc.ClientDriver";
this.url = "jdbc:derby://localhost:1527/used_car;create = true";
this.user = "root";
this.password = "wzj";
try{
Class.forName(DBDriver);//加载驱动
conn = DriverManager.getConnection(url,user,password);//建立连接
stmt = conn.createStatement();//获取访问对象
}catch(ClassNotFoundException e){
e.printStackTrace();
}catch(SQLException e){
e.printStackTrace();
}
}
//需要传参数的公用访问
public InitDB(String DBDriver,String url,String user,String password){
this.DBDriver = DBDriver;
this.url = url;
this.user = user;
this.password = password;
try{
Class.forName(DBDriver);
conn = DriverManager.getConnection(url,user,password);
stmt = conn.createStatement();
}catch(ClassNotFoundException e){
e.printStackTrace();
}catch(SQLException e){
e.printStackTrace();
}
}
public static InitDB getInitDB(){
if(initDB_obj==null)
initDB_obj = new InitDB();
return initDB_obj;
}
public Connection getConn(){
return conn;
}
public Statement getStmt(){
return stmt;
}
public ResultSet getRs(String sql){//获取查询结果集
if(sql.toLowerCase().indexOf("select")!= -1){
try{
rs = stmt.executeQuery(sql);
}catch(SQLException e){
//TODO Auto-generated catch block
e.printStackTrace();
}
}
return rs;
}
public void closeDB(){//关闭连接，释放资源
try{
if(rs!= null){
rs.close();
}
if(stmt!= null){
stmt.close();
}
if(conn!= null){
conn.close();
}
}catch(SQLException e){
e.printStackTrace();
}
}
}
运行结果,总是出现这种错误。