使用Ｃursor时出现source not found

Question

import android.database.Cursor;Cursor c=db.query("tb_user",null,null,null,null,null,null);
            
            int id;
            String username;
            String password;
            if(c.moveToFirst())
            {
 
                  for(int i=0;i<c.getCount();i++)
                  {
                        c.move(i);                        
                        id=c.getInt(0);                        
                        username=c.getString(1);
                        password=c.getString(2);
                        res += username;                  }            }
debug的时候用f6单步调试可以跑完程序没事，如果不设断点直接跑就会出现Class File Editor 
source not found
The JAR file xxx\android.jar has no source attachment我新手一名。谢谢。