可以用commons-collection中的Bag或者MultiValueMap,不过效率不高.
用java的Map放Integer主要问题在于Integer是不可变类,每次需要构造新的对象,开销比较大,因此尝试了common-lang中的MutableInt和java.util中的AtomicInteger,这俩的效率不相上下.
不过最快的方式是在Map中放int数组...不过优势也不是特别明显
int size = 10000000; // 1 long start = System.currentTimeMillis(); Bag bag = BagUtils.typedBag(new HashBag(), String.class); for (int i = 0; i < size; i++) { bag.add("" + (i % 100), 1); } System.out.println(bag.getCount("5")); System.out.println(System.currentTimeMillis() - start); // 2 start = System.currentTimeMillis(); MultiValueMap map = new MultiValueMap(); for (int i = 0; i < size; i++) { map.put("" + (i % 100), 1); } int total = 0; Collection<Integer> co = (Collection<Integer>) map.get("5"); for (Integer i : co) { total += i; } System.out.println(total); System.out.println(System.currentTimeMillis() - start); // 3 start = System.currentTimeMillis(); Map<String, AtomicInteger> map3 = new HashMap<>(); for (int i = 0; i < size; i++) { String key = "" + (i % 100); AtomicInteger value = map3.get(key); if (value == null) { map3.put(key, new AtomicInteger(1)); } else { value.addAndGet(1); } } System.out.println(map3.get("5")); System.out.println(System.currentTimeMillis() - start); // 4 start = System.currentTimeMillis(); Map<String, MutableInt> map4 = new HashMap<>(); for (int i = 0; i < size; i++) { String key = "" + (i % 100); MutableInt value = map4.get(key); if (value == null) { map4.put(key, new MutableInt(1)); } else { value.add(1); } } System.out.println(map4.get("5")); System.out.println(System.currentTimeMillis() - start); // 5 start = System.currentTimeMillis(); Map<String, Integer> map5 = new HashMap<>(); for (int i = 0; i < size; i++) { String key = "" + (i % 100); Integer value = map5.get(key); if (value == null) { map5.put(key, new Integer(1)); } else { map5.put(key, value + 1); } } System.out.println(map5.get("5")); System.out.println(System.currentTimeMillis() - start); // 6 start = System.currentTimeMillis(); Map<String, int[]> map6 = new HashMap<>(); for (int i = 0; i < size; i++) { String key = "" + (i % 100); int[] value = map6.get(key); if (value == null) { map6.put(key, new int[] { 1 }); } else { value[0] += 1; } } System.out.println(map6.get("5")[0]); System.out.println(System.currentTimeMillis() - start);