java 小数点取2位并且四舍五入

BigDecimal bd = new BigDecimal(0.0199999999999);
System.out.println("res:"+bd.setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue());

         DecimalFormat df = new DecimalFormat("#.00");
         System.out.println(df.format(Double.parseDouble(str)));
         System.out.println("=================");
         System.out.println(String.format("%.2f", Double.parseDouble(str)));
         System.out.println("=================");
         NumberFormat nf = NumberFormat.getNumberInstance();
         nf.setMaximumFractionDigits(2);
         System.out.println(nf.format(Double.parseDouble(str)));