若是父類實現並重寫了compareTo方法，那麼其子類一樣具備該方法，能夠直接加入TreeSet

class Person implements Comparable<Person> { String name; public Person(String name) { this.name = name; } @Override public int compareTo(Person o) { return (this.name.compareTo(o.name) == 0) ? this.g

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