public boolean equals(Object obj) {
        if (obj == this) {
            return true;   
        }
        if (!(obj instanceof DefaultStatisticalCategoryDataset)) {
            return false;   
        }
        DefaultStatisticalCategoryDataset that 
                = (DefaultStatisticalCategoryDataset) obj;
        if (!this.data.equals(that.data)) {
            return false;   
        }
        return true;