JTextComponent: there is some inconsistency between following methods. In particular, second one checks for null whereas first do not.
Moreover, I'd reuse the code like this:
    public void selectAll() {
        if (doc != null) {
            select(0, getDocument().getLength());
        }
    }

---------
    public void select(int selectionStart, int selectionEnd) {
        // argument adjustment done by java.awt.TextComponent
        int docLength = getDocument().getLength();

        [...some bounds math...]
        setCaretPosition(selectionStart);
        moveCaretPosition(selectionEnd);
    }

    /**
     * Selects all the text in the <code>TextComponent</code>.
     * Does nothing on a <code>null</code> or empty document.
     */
    public void selectAll() {
        Document doc = getDocument();
        if (doc != null) {
            setCaretPosition(0);
            moveCaretPosition(doc.getLength());
        }
    }