存档--浮点型计算
add

float amount = 501.8;BigDecimal b = new BigDecimal(Float.toString(amount));amount = b.add(new BigDecimal(request.getParameter("price").trim())).floatValue();

subtract

float amount = 501.8;BigDecimal b = new BigDecimal(Float.toString(amount));amount = b.subtract(new BigDecimal(request.getParameter("price").trim())).floatValue();

注意：传进去new BigDecimal 的是 String类型。否则同样会丢失精度的问题。
如:

public static void main(String[] args) {float a = 501.8f;float b = 500f;System.out.println(a-b);BigDecimal c = new BigDecimal(a);a = c.subtract(new BigDecimal(b)).floatValue();System.out.println(a);}

输出结果:都是1.7999878
只有

public static void main(String[] args) {float a = 501.8f;float b = 500f;System.out.println(a-b);BigDecimal c = new BigDecimal(Float.toString(a));a = c.subtract(new BigDecimal(Float.toString(b))).floatValue();System.out.println(a);}

输出结果:1.7999878
1.8