今天在專案中遇到一個奇怪的現象

Double doubleValue = new BigDecimal("0.02").subtract(new BigDecimal(0.02)).doubleValue();

預計出現的結果是0.0

可是通過打印出現的結果是-4.163336342344337E-19

在網上找了很多資料，都是說BigDecimal的構造建議用string，自己也試了下利用string構造也不會出問題

最後在double引數的構造上看到這一段註釋：
     The results of this constructor can be somewhat unpredictable.
     * One might assume that writing {@code new BigDecimal(0.1)} in
     * Java creates a {@code BigDecimal} which is exactly equal to
     * 0.1 (an unscaled value of 1, with a scale of 1), but it is
     * actually equal to
     * 0.1000000000000000055511151231257827021181583404541015625.
     * This is because 0.1 cannot be represented exactly as a
     * {@code double} (or, for that matter, as a binary fraction of
     * any finite length).  Thus, the value that is being passed
     * <i>in</i> to the constructor is not exactly equal to 0.1,
     * appearances notwithstanding.

大概的意識就是說double會出現精度缺失，不建議使用！所以以後還是用String吧