将多个集合合并为一个集合，并删除重复的集合

Question

我有m个集合，可以使用array或arraylist来存储。这些集合之间存在重叠。我想把这m个集合合并成一个集合，而那些重复的元素只会占据组合集合中的一个位置。我应该使用哪种数据结构和操作来构造组合集。

Answer 1

下面的代码将为您完成此操作：

    Set set = new HashSet();
    ArrayList list = new ArrayList();
    ArrayList list2 = new ArrayList(); //etc
    Object[] array = new Object[]{};
    Object[] array2 = new Object[]{}; // etc
    set.addAll(list);
    set.addAll(list2);
    set.addAll(Arrays.asList(array));
    set.addAll(Arrays.asList(array2));
    // Call addAll as many times as you like

set现在包含所有唯一值，每个值一次

Answer 2

请参阅: java.util.Set.addAll(Collection)：的javadoc

/**
 * Adds all of the elements in the specified collection to this set if
 * they're not already present (optional operation).  If the specified
 * collection is also a set, the <tt>addAll</tt> operation effectively
 * modifies this set so that its value is the <i>union</i> of the two
 * sets.  The behavior of this operation is undefined if the specified
 * collection is modified while the operation is in progress.

Answer 3

/**
 * Join multiple sets into one.
 */
@SafeVarargs
private final <T> Set<T> join(Set<T>... sets)
{
    Set<T> result = new HashSet<>();
    if (sets == null)
        return result;

    for (Set<T> set : sets)
    {
        if (set != null)
            result.addAll(set);
    }
    return result;
}