解决前：

    1. BigDecimal amout3=new BigDecimal(0.02);
    2. BigDecimal amout4=new BigDecimal(0.03);
    3. System.out.println(amout4.subtract(amout3));

    结果为：0.0099999999999999984734433411404097569175064563751220703125

    解决后：

    1. BigDecimal amout1=BigDecimal.valueOf(0.02);
    2. BigDecimal amout2=BigDecimal.valueOf(0.03);
    3. System.out.println(amout2.subtract(amout1));

    结果为：0.01