public class A extends JPanel
{
   private JTextField jtf;

   public A()
   {
       jtf = new JTextField();
       ...setting size and positions...
       add(jtf);
      
   }

   class VerySpecificJTF extends SpecificJTF 
   {
      public VerySpecificJTF (){}
   }
}

=========class in another file===============
abstract public class SpecificJTF extends JTextField
{
   ...some code...
}

}

public class A extends JPanel
{
   private VerySpecificJTF jtf;

   public A()
   {
       jtf = new VerySpecificJTF();
       ...setting size and positions...
       add(jtf);
      
   }

   class VerySpecificJTF extends SpecificJTF 
   {
      public VerySpecificJTF (){}
   }
}

public abstract class PatternPanel extends JPanel
{
public JCheckBox isActive;
abstract void someMethod();
...
}

===== PatternPanel.java ================
public abstract class PatternPanel extends JPanel
{
public JCheckBox isActive;     //should be this panel active or not
abstract void someMethod();
}

===== SpecificPanel.java ================
public SpecificPanel extends PatternPanel 
{
//JCheckBox isActive = new JCheckBox();    //isActive will be showed but for me this is useless
public SpecificPanel()
{isActive = new JCheckBox();  //isActive will not be showed on SpecifecPanel in design view. How to do that design wiev will show this component?
isActive.setEnabled(true);
}

void someMethod(){};

public abstract class PatternPanel extends JPanel {
	public JCheckBox isActive = new JCheckBox();
	public PatternPanel() {
		add(isActive);
	}
	abstract void someMethod();
}

public class SpecificPanel extends PatternPanel {
	public SpecificPanel() {
		isActive.setEnabled(true);
	}
	void someMethod() {
	};
}