Java项目Guava包 HashMultimap使用及注意事项

abstract class AbstractMapBasedMultimap<K, V> extends AbstractMultimap<K, V> implements Serializable {
    private transient Map<K, Collection<V>> map;
}

private HashMultimap(int expectedKeys, int expectedValuesPerKey) {
    super(Platform.newHashMapWithExpectedSize(expectedKeys));
    this.expectedValuesPerKey = 2;
    Preconditions.checkArgument(expectedValuesPerKey >= 0);
    this.expectedValuesPerKey = expectedValuesPerKey;
}

private HashMultimap(Multimap<? extends K, ? extends V> multimap) {
    super(Platform.newHashMapWithExpectedSize(multimap.keySet().size()));
    this.expectedValuesPerKey = 2;
    this.putAll(multimap);
}

public boolean put(@Nullable K key, @Nullable V value) {
    Collection<V> collection = (Collection)this.map.get(key);
    if (collection == null) {
        collection = this.createCollection(key);
        if (collection.add(value)) {
            ++this.totalSize;
            this.map.put(key, collection);
            return true;
        } else {
            throw new AssertionError("New Collection violated the Collection spec");
        }
    } else if (collection.add(value)) {
        ++this.totalSize;
        return true;
    } else {
        return false;
    }
}

// com.google.common.collect.HashMultimap#createCollection
Set<V> createCollection() {
    return Platform.newHashSetWithExpectedSize(this.expectedValuesPerKey);
}

// 创建一个默认的 HashMap<String, Set<Integer>>，容器的初始化容量与HashMap的默认值一样
HashMultimap<String, Integer> map = HashMultimap.create();

// 当我们知道容器的个数时，推荐使用下面这种方式, 
// HashMap 设置容量为8, 每个HashSet的容量初始化为16
HashMultimap<String, Integer> map2 = HashMultimap.create(8, 16);

// 另外一个就是基于MultMap来创建的case了
HashMultimap<String, Integer> map3 = HashMultimap.create(map);

// 添加单个元素
map.put("hello", 510);
// 添加多个元素
map.putAll("skill", Arrays.asList(1, 2, 3, 4, 1));

// 移除skill对应的集合中，value=3的元素
map.remove("skill", 3);
// 移除key
map.removeAll("hello");

// 直接替换skill对应的value集合，新的值为 {100, 200, 300}
map.replaceValues("skill", Arrays.asList(100, 200, 300));

// 获取对应的value集合，当不存在时，返回空集合（不是null，简直是贴心）
Set<Integer> set = map.get("skill");

for (Map.Entry<String, Integer> entry: map.entries()) {
    System.out.println(entry.getKey() + ":" + entry.getValue());
}

// 输出所有的key，
map.keys()
// 输出key集合
map.keySet();

HashMultimap<String, Integer> map = HashMultimap.create();
map.replaceValues("skill", Arrays.asList(100, 200, 300));
System.out.println("keys=" + map.keys());
System.out.println("keySet=" + map.keySet());

HashMultimap<String, Integer> map = HashMultimap.create();
map.putAll("skill", Arrays.asList(100, 200, 300));
map.put("a", 100);
for (Integer v: map.values()) {
    System.out.println(v);
}