One of the most useful behaviors you can give to quantities is to provide printing and parsing methods that allow you easily produce strings and to produce a quantity from a string.

• 我们可以给数量添加的最有用的行为之一就是为其提供打印和解析方法，这让我们很容易生成数量的字符串表达，也可以将字符串解析成数量。