Guava工具类中一些集合和方法的使用

Multiset：无序可重复set，重复元素显示个数 还是挺有用的数据结构

　　 @Test
    void test5() {
        String s = "good good study day day up";
        String[] s1 = s.split(" ");
        HashMultiset<String> multiset = HashMultiset.create();
        multiset.addAll(Arrays.asList(s1));
        System.out.println(multiset);//[study, up, good x 2, day x 2]
        multiset.forEach(e -> {
            System.out.println(e + "->" + multiset.count(e));
            /*
            study->1
            up->1
            good->2
            good->2
            day->2
            day->2
            */
        });
    }

Multimap：key可重复的map（我理解就是Map<String, Set<String>这种结构）

　@Test
　void test6() {
    //需求：统计每个作者有几本书
    HashMap<String, String> map = new HashMap<>();
    map.put("Java从入门到精通", "bin");  //书名：作者
    map.put("Java从入门到精通", "bin");  //书名：作者
    map.put("Android从入门到精通", "bin");  //书名：作者
    map.put("PHP从入门到精通", "jack");  //书名：作者
    map.put("笑看人数", "vince");  //书名：作者

    Multimap<String, String> mmap = ArrayListMultimap.create();
    Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();
    while (iterator.hasNext()) {
        Map.Entry<String, String> next = iterator.next();
        mmap.put(next.getValue(), next.getKey());
    }
    System.out.println(mmap);//{bin=[Java从入门到精通, Android从入门到精通], vince=[笑看人数], jack=[PHP从入门到精通]}
    Set<String> strings = mmap.keySet();
    strings.forEach(e -> {
        System.out.println(e + " -> " +mmap.get(e));
    });

　　/**
 　　* bin -> [Java从入门到精通, Android从入门到精通]
 　　* vince -> [笑看人数]
 　　* jack -> [PHP从入门到精通]
 　　*/

}

BiMap: 可以反转的map, key相同插入会覆盖之前的。（适用场景：手机号和微信号一对一）

    @Test
    void test1() {
        BiMap<String, String> biMap = HashBiMap.create();
        biMap.put("13453455561", "wx132131");
        biMap.put("13453455562", "wx132132");
        biMap.put("13453455563", "wx132133");
        biMap.put("13453455563", "wx132134");
        System.out.println(biMap); //{13453455561=wx132131, 13453455562=wx132132, 13453455563=wx132134}
        System.out.println(biMap.get("13453455561"));//wx132131
        BiMap<String, String> inverse = biMap.inverse();
        System.out.println(inverse.get("wx132131"));//13453455561
        System.out.println(inverse);//{wx132131=13453455561, wx132132=13453455562, wx132134=13453455563}
        System.out.println(biMap.inverse().inverse() == biMap);//true
    }

 

求集合交集、并集、差集，非常好用

　　 @Test
    void test4() {
        HashSet<Integer> set1 = Sets.newHashSet(1, 2, 3);
        HashSet<Integer> set2 = Sets.newHashSet(3, 4, 5);
        Sets.SetView<Integer> intersection = Sets.intersection(set1, set2);
        System.out.println(intersection); //[3]

        Sets.SetView<Integer> difference = Sets.difference(set1, set2);
        System.out.println(difference);//[1, 2]

        Sets.SetView<Integer> union = Sets.union(set1, set2);
        System.out.println(union);//[1, 2, 3, 4, 5]
    }

未完待续......