个人认为不错的代码结构：利用switch case语句进行参数的取值校验

    public void setHorizontalScrollBarPolicy(int policy) {        switch (policy) {        case HORIZONTAL_SCROLLBAR_AS_NEEDED:        case HORIZONTAL_SCROLLBAR_NEVER:        case HORIZONTAL_SCROLLBAR_ALWAYS:                break;        default:            throw new IllegalArgumentException("invalid horizontalScrollBarPolicy");        }        int old = horizontalScrollBarPolicy;        horizontalScrollBarPolicy = policy;        firePropertyChange("horizontalScrollBarPolicy", old, policy);        revalidate();        repaint();    }