The following sample demonstrates how to add and remove range comments.

import com.jniwrapper.win32.automation.IDispatch;
import com.jniwrapper.win32.automation.types.Variant;
import com.jniwrapper.win32.excel.Comment;
import com.jniwrapper.win32.excel.Range;
import com.jniwrapper.win32.excel._Worksheet;
import com.jniwrapper.win32.excel.impl.RangeImpl;
import com.jniwrapper.win32.jexcel.Application;
import com.jniwrapper.win32.jexcel.Workbook;
import com.jniwrapper.win32.jexcel.Worksheet;

import java.io.File;

public class RangeCommentSample {
    public static final String comment = "My comment";

    public static void main(String[] args) throws Exception {
        Application application = new Application();
        Workbook workbook = application.openWorkbook(new File("comment.xls"));
        Worksheet markedSheet = workbook.getWorksheet(1);
        final _Worksheet worksheetPeer = markedSheet.getPeer();
        markedSheet.getOleMessageLoop().doInvokeAndWait(new Runnable() {
            @Override
            public void run() {
                Range worksheetCells = worksheetPeer.getCells();
                long row = 1;
                long column = 1;

                IDispatch rangeDispatch = worksheetCells.getItem(new Variant(row), new Variant(column)).getPdispVal();
                Range range = new RangeImpl(rangeDispatch);

                com.jniwrapper.win32.excel.Comment currentComment = range.getComment();

                String newComment = comment;

                if (currentComment != null && !currentComment.isNull()) {
                    Variant unspecified = Variant.createUnspecifiedParameter();

                    newComment = currentComment.text(unspecified, unspecified, unspecified) + "\n" + comment;

                    // delete old comment: Excel does not allow to add a comment if a
                    // comment already exists for a particular cell
                    currentComment.delete();
                    currentComment.setAutoDelete(false);
                    currentComment.release();
                }

                final String commentToBeAdded = newComment;
                System.out.println("commentToBeAdded = " + commentToBeAdded);

                // create a new comment for this cell
                Comment addedComment = range.addComment(new Variant(commentToBeAdded));
                addedComment.setAutoDelete(false);
                addedComment.release();

                range.setAutoDelete(false);
                range.release();
                rangeDispatch.setAutoDelete(false);
                rangeDispatch.release();
                worksheetCells.setAutoDelete(false);
                worksheetCells.release();
            }
        });

        workbook.save();
        application.close(true);
    }
}