Why are my checkboxes created as buttons Java

I've added a few checkboxes using WindowBuilder and instead of them being checkboxes they appear as buttons in my code. Why is that? Do I treat them as normal buttons? How do I group them? Can I do Group grpExtensions = new Group(shlProgram, SWT.NONE);

This is how checkboxes are initialised

Group grpExtensions = new Group(shlDriveassistAutotagger, SWT.NONE);
grpExtensions.setText("Extensions to Auto-tag");
grpExtensions.setBounds(10, 10, 165, 189);

Button btnpdf = new Button(grpExtensions, SWT.CHECK);
btnpdf.addSelectionListener(new SelectionAdapter() {
    @Override
    public void widgetSelected(SelectionEvent e) {

    }
});
btnpdf.setBounds(10, 21, 49, 16);
btnpdf.setText(".pdf");