[Java基礎]讓Map value自增

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需求：我要在map中判斷是否存在key，存在則讓key對應的value = value+1，否則設定<key，value=1>

代碼實現方式如下：

ContainsKey

import java.util.HashMap;import java.util.Map;...Map<String, Integer> freq = new HashMap<String, Integer>();...int count = freq.containsKey(word) ? freq.get(word) : 0;freq.put(word, count + 1);

TestForNull

import java.util.HashMap;import java.util.Map;...Map<String, Integer> freq = new HashMap<String, Integer>();...Integer count = freq.get(word);if (count == null) {    freq.put(word, 1);}else {    freq.put(word, count + 1);}

AtomicLong

import java.util.concurrent.ConcurrentHashMap;import java.util.concurrent.ConcurrentMap;import java.util.concurrent.atomic.AtomicLong;...final ConcurrentMap<String, AtomicLong> map =     new ConcurrentHashMap<String, AtomicLong>();...map.putIfAbsent(word, new AtomicLong(0));map.get(word).incrementAndGet();

Trove

import gnu.trove.TObjectIntHashMap;...TObjectIntHashMap<String> freq = new TObjectIntHashMap<String>();...freq.adjustOrPutValue(word, 1, 1);

MutableInt

import java.util.HashMap;import java.util.Map;...class MutableInt {  int value = 1; // note that we start at 1 since we‘re counting  public void increment () { ++value;      }  public int  get ()       { return value; }}...Map<String, MutableInt> freq = new HashMap<String, MutableInt>();...MutableInt count = freq.get(word);if (count == null) {    freq.put(word, new MutableInt());}else {    count.increment();}

還有Java8的方法：  

Map.merge(key, 1, Integer::sum) //如果key存在，就調用sum 1 到map的value，如果key不存在，put（key，1）

時間方面，執行1000次數，如下所示

                 time, mskolobokeCompile  18.8koloboke         19.8trove            20.8fastutil         22.7mutableInt       24.3atomicInteger    25.3eclipse          26.9hashMap          28.0hppc             33.6hppcRt           36.5

 

[Java基礎]讓Map value自增