Java：按顺序包含唯一元素的列表

Question

Is there a list type in java that stores objects in ascending order and not adds if this object is previously added. I know java maps can do that but I wonder if there is a list type that does what I want. Otherwise I have to override contains, equalsTo and add methods,right?

Answer 1

So you need a list containing only unique elements? Two options:

• java.util.LinkedHashSet - preserves the order of insertion, has the set semantics
• from commons-collections SetUniqueList - allows list operations like get(..) and set(..)
• from commons-collections ListOrderedSet

Answer 2

Depends on what order do you mean.

• Sorting order - use TreeSet
• Order of insertion - use LinkedHashSet

Answer 3

TreeSet will do the trick. Example :

SortedSet<Integer> myOrderedUniqueList = new TreeSet<Integer>()

Answer 4

I think you're after a SortedSet (this is an interface which extends Set). Set is like a List but it contains only one of each value.

TreeSet is a commonly-used implementation of SortedSet

http://download.oracle.com/javase/6/docs/api/java/util/TreeSet.html

Answer 5

SortedSet is a subinterface of Set, which guarantees that the elements in the set are sorted.

SortedSet<Integer> orderedSet = new TreeSet<Integer>();

Use them when you have to stores non-duplicate elements in increasing order of the element values

Answer 6

TreeSet might be exactly what you need.

It stores the elements in a sorted tree. So you can iterate over them in sorted order. It's not a list, but it performs better with respect to add and contains.

Answer 7

使用 java.util.LinkedHashSet 与覆盖 hashCode() 和 equals(Object obj) 使用唯一属性

Answer 8

public static <T> List<T> getUniqueListOrdered(List<T> values) {
    Set<T> uniqueValues = new HashSet<>();
    return values.stream().filter(value -> uniqueValues.add(value)).collect(Collectors.toList());
}


@Test
public void createUnique() {
    List<String> unique = ListUtils.getUniqueListOrdered(Arrays.asList("A", "A", "A", "B", "B"));
    Assert.assertEquals(unique, Arrays.asList("A", "B"));
}

Answer 9

它不是一个列表，但您可以查看 Sethttp://download.oracle.com/javase/6/docs/api/java/util/Set.html 的实现