Guava集合(一)新的集合類型篇

Guava引入了許多新的收集類型，這些類型不在JDK中，但是卻十分有用。

Multiset

Multiset允許集合中插入重複的元素，Multiset只是一個實現類，其實現類有：

Multiset子類	是否支持空元素
HashMultiset	Yes
TreeMultiset	Yes
LinkedHashMultiset	Yes
ConcurrentHashMultiset	Yes
ConcurrentHashMultiset	No
ConcurrentHashMultiset	No

示例：

   @Test
    public void testMultiSet () {
        Multiset<String> multiset = HashMultiset.create();
        multiset.addAll( Lists.newArrayList("I","love","China","China","is","my","love"));
        multiset.count("love");//2
        multiset.count("I");//1
        Set<String> elementSet = multiset.elementSet();
        System.out.println(elementSet);//[love, China, I, is, my]
        Set<Multiset.Entry<String>> entries = multiset.entrySet();//統計元素頻次
        System.out.println(entries);//[love x 2, China x 2, I, is, my]
    }

SortedMultiset

SortedMultiset是能排序的multiSet，它只是一個接口，能夠按照範圍篩選子集，其實現類有TreeMultiset。

    @Test
    public void testTreeMultiset () {
//        TreeMultiset.create(Ordering.natural()); 默認就是字典序
        SortedMultiset<String> sortedMultiset = TreeMultiset.create();
        sortedMultiset.addAll( Lists.newArrayList("I","love","China","China","is","my","love"));
        sortedMultiset.count("love");//2
        sortedMultiset.count("I");//1
        Set<String> elementSet = sortedMultiset.elementSet();
        System.out.println(elementSet);//[China, I, is, love, my]
        Set<Multiset.Entry<String>> entries = sortedMultiset.entrySet();
        // 可以看到和HashMutiSet的區別，元素排好序了
        System.out.println(entries);//[China x 2, I, is, love x 2, my]
        // 按範圍篩選子集合
        SortedMultiset<String> subMultiset = sortedMultiset.subMultiset("I", BoundType.CLOSED, "lovv", BoundType.OPEN);
        System.out.println(subMultiset);//[I, is, love x 2]
    }

Multimap

Multimap 用於key值相同value值不同的場景，即同一個key值有多個value

Implementation	Keys behave like…	Values behave like…
ArrayListMultimap	HashMap	ArrayList
HashMultimap	HashMap	HashSet
LinkedListMultimap	LinkedHashMap	* LinkedList*
LinkedHashMultimap	LinkedHashMap	LinkedHashSet
TreeMultimap	TreeMap	TreeSet
ImmutableListMultimap	ImmutableMap	ImmutableList
ImmutableSetMultimap	ImmutableMap	ImmutableSet

ArrayListMultimap示例：

    @Test
    public void testArrayListMultimap() {
//        value 值允許重複 類似於list
        Multimap<Object, Object> multimap = ArrayListMultimap.create();
        multimap.put("a","aa");
        multimap.put("a","aaa");
        multimap.put("b","bb");
        multimap.put("b","bbb");
        multimap.put("b","bbb");
        System.out.println(multimap);//{a=[aa, aaa], b=[bb, bbb]}
    }

HashMultimap 示例：

    @Test
    public void testHashMultimap() {
//        value 值不允許重複 類似於set
        Multimap<Object, Object> multimap = HashMultimap.create();
        multimap.put("a","aa");
        multimap.put("a","aaa");
        multimap.put("b","bb");
        multimap.put("b","bbb");
        multimap.put("b","bbb");
        System.out.println(multimap);//{a=[aa, aaa], b=[bb, bbb]}
    }

BiMap

雙向映射，value值是唯一的 不允許重複，如果添加的value值已經存在了會報錯。

    @Test
    public void testBiMap() {
//        value 值不允許重複 類似於set
        BiMap<Object, Object> biMap = HashBiMap.create();
        biMap.put("1","a");
//        biMap.put("2","a"); //拋出異常，java.lang.IllegalArgumentException: value already present: a
        System.out.println(biMap.get("1"));//a
//        biMap.inverse();
        System.out.println(biMap.inverse().get("a"));//1
    }

Table

@Test
public void testTable (){
Table<String, String, Double> weightedGraph = HashBasedTable.create();
weightedGraph.put(“v1”, “v2”, 4D);
weightedGraph.put(“v1”, “v3”, 20d);
weightedGraph.put(“v2”, “v3”, 5d);

    weightedGraph.row("v2"); // returns a Map mapping v2 to 4, v3 to 20
    weightedGraph.column("v3"); // returns a Map mapping v1 to 20, v2 to 5
}

RangeSet

 @Test
    public void testRangeSet (){
        RangeSet<Integer> rangeSet = TreeRangeSet.create();
        rangeSet.add(Range.closed(1, 10)); // {[1, 10]}
        rangeSet.add(Range.closedOpen(11, 15)); // disconnected range: {[1, 10], [11, 15)}
        rangeSet.add(Range.closedOpen(15, 20)); // connected range; {[1, 10], [11, 20)}
        rangeSet.add(Range.openClosed(0, 0)); // empty range; {[1, 10], [11, 20)}
        rangeSet.remove(Range.open(5, 10)); // splits [1, 10]; {[1, 5], [10, 10], [11, 20)}
        rangeSet.rangeContaining(2);//Range [1,5]
        rangeSet.rangeContaining(6);//null
    }