XMLGregorianCalendar objects are mutable, and therefore you can simply set any of the date or time fields directly on the object.

XMLGregorianCalendar对象是可以修改的，因此能够直接设置对象的日期或时间字段。

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Lists, specifically, are handy mutable objects that can conveniently even hold multiple values.

明确的讲，列表是一些便利的可变对象，他们甚至可以方便地保留多个值。

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Some design problems are easier to solve with mutable objects.

有一些设计问题还是使用易变对象比较容易解决。

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