第213題

Given a class whose instances, when found in a collection of objects, are sorted by using the compareTo() method, which two statements are true? (choose two.)
A. The class implements java.lang.Comparable.
B. The class implements java.util.Comparator.
C. The interface used to implement sorting allows this class to define only one sort sequence.
D. The interface used to implement sorting allows this class to define many different sort sequences.
答案：AC
參考：12-4-3 SortedSet集合

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實作Comparable,並實作compareTo()的內容.
實作排序方法只能用一種排序方法. (實作順序,就不能用逆序).