EDIT

package eu.etaxonomy.taxeditor.molecular.handler;

import org.eclipse.core.commands.AbstractHandler;

import org.eclipse.core.commands.ExecutionEvent;

import org.eclipse.core.commands.ExecutionException;

import org.eclipse.swt.dnd.Clipboard;

import org.eclipse.swt.dnd.TextTransfer;

import org.eclipse.swt.dnd.Transfer;

import org.eclipse.swt.widgets.Display;

import org.eclipse.ui.IEditorPart;

import org.eclipse.ui.handlers.HandlerUtil;

import eu.etaxonomy.taxeditor.molecular.editor.AlignmentEditor;

public class AlignmentEditorCopyHandler extends AbstractHandler {

    @Override

    public Object execute(ExecutionEvent event) throws ExecutionException {

        Clipboard clipboard = new Clipboard(Display.getCurrent());

        TextTransfer textTransfer = TextTransfer.getInstance();

        Transfer[] transfers = new Transfer[]{textTransfer};

        String selectedSequenceString = "Blabla";

        IEditorPart activeEditor = HandlerUtil.getActiveEditor(event);

        if(activeEditor instanceof AlignmentEditor){

            AlignmentEditor alignmentEditor = (AlignmentEditor)activeEditor;

            //TODO get selected sequence string

        }

        Object[] data = new Object[]{selectedSequenceString};

        clipboard.setContents(data, transfers);

        return null;

    }

}