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Basic Java and Tools - Pumpkinor.io
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<h1>数值计算-精度，舍入和溢出</h1>
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<h4><a id="%E6%91%98%E5%BD%95" class="anchor" aria-hidden="true"><span class="octicon octicon-link"></span></a>摘录</h4>
<p>浮点数的表示、计算、舍入和格式化、溢出等涉及的一些坑：</p>
<ol>
<li>切记，要精确表示浮点数应该使用 BigDecimal。并且，使用 BigDecimal 的 Double 入参的构造方法同样存在精度丢失问题，应该使用 String 入参的构造方法或者 BigDecimal.valueOf 方法来初始化。</li>
<li>对浮点数做精确计算，参与计算的各种数值应该始终使用 BigDecimal，所有的计算都要通过 BigDecimal 的方法进行，切勿只是让 BigDecimal 来走过场。任何一个环节出现精度损失，最后的计算结果可能都会出现误差。</li>
<li>对于浮点数的格式化，如果使用 String.format 的话，需要认识到它使用的是四舍五入，可以考虑使用 DecimalFormat 来明确指定舍入方式。但考虑到精度问题，我更建议使用 BigDecimal 来表示浮点数，并使用其 setScale 方法指定舍入的位数和方式。</li>
<li>进行数值运算时要小心溢出问题，虽然溢出后不会出现异常，但得到的计算结果是完全错误的。我们考虑使用 Math.xxxExact 方法来进行运算，在溢出时能抛出异常，更建议对于可能会出现溢出的大数运算使用 BigInteger 类。</li>
</ol>
<p>总之，对于金融、科学计算等场景，请尽可能使用 BigDecimal 和 BigInteger，避免由精度和溢出问题引发难以发现，但影响重大的 Bug。</p>
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<span class="date">2021/10/22</span>
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