C#

public abstract class ReallyAbstractBase
{
  int _value;
  public ReallyAbstractBase(int value)
  {
    _value = value;
  }
  public int Value
  {
    get { return _value ; }
  }

  public abstract void DoSomething() ;
}

public abstract class MyAbstract : ReallyAbstractBase
{
  protected string _text;
  public MyAbstract(int value) : this(value, string.Empty) {}
  public MyAbstract(int value, string text) : base(value)
  {
    _text = text;
  }
  public virtual void DoSomething()
  {
    throw new Exception("Not implemented");
  }
}

public class ConcreteClass : MyAbstract
{
  public ConcreteClass() : this(0, string.Empty) {}
  public ConcreteClass(int value) : this(value, string.Empty) {}
  public ConcreteClass(string text) : this(0, text) {}
  public ConcreteClass(int value, string text) : base(value, text) {}

  public virtual void DoSomething()
  {
    Console.WriteLine("Do something called");
  }
}

public abstract class MyAbstract : ReallyAbstractBase
    {
        protected string _text;
        public MyAbstract(int value) : this(value, string.Empty) { }
        public MyAbstract(int value, string text)
            : base(value)
        {
            _text = text;
        }
        public override abstract void DoSomething();
        
    }

    public class ConcreteClass : MyAbstract
    {
        public ConcreteClass() : this(0, string.Empty) { }
        public ConcreteClass(int value) : this(value, string.Empty) { }
        public ConcreteClass(string text) : this(0, text) { }
        public ConcreteClass(int value, string text) : base(value, text) { }

        public override void DoSomething()
        {
            Console.WriteLine("Do something called");
        }
    }

<br />
object locker = new object();<br />
 private void opg_filter_functie()<br />
{<br />
lock(locker) {<br />
//check if textbox isnt empty<br />
if (opg_filterbox.Text.Length > 0)<br />
{<br />
try<br />
{<br />
opg_tv_filter.Nodes.Clear();<br />
//sql injection causes error fix<br />
opg_filterbox.Text = opg_filterbox.Text.Replace("'", "");<br />
//create query<br />
<br />
SqlDataAdapter dAdapter = new SqlDataAdapter("SELECT artiestNaam FROM artiest where artiestnaam like '" + opg_filterbox.Text + "%'" ,sqlcon);<br />
DataSet dataset_filter = new DataSet();<br />
<br />
<br />
dAdapter.Fill(dataset_filter); //crash here if typing to fast <br />
}