// 1.無參數構造方法new ConcurrentHashMap();// 2.指定初始容量new ConcurrentHashMap(initialCapacity)// 3.指定初始容量和加載因子new ConcurrentHashMap(initialCapacity,loadFactor)// 4.指定初始容量和加載因子與并發級別(并發更新線程數)new ConcurrentHashMap(initialCapacity, loadFactor, concurrencyLevel)// 5.創建與給定映射具有相同映射的新映射new ConcurrentHashMap(Map<? extends K, ? extends V> m)方法介紹

新增元素

// 1.添加元素，不允許nullmap.put(1,1);// 2.添加一個mapmap.putAll(map);// 3.添加元素, 鍵不存在映射關系才添加成功map.putIfAbsent(2,1);

刪除元素

// 1.移除指定的keymap.remove(1);// 2.移除指定的key,value map.remove(2,2);

替換元素

// 1.替換指定keymap.replace(1,3);// 2.替換指定key,valuemap.replace(1,2,4);// 3.替換所有，這里是把value都乘以2map.replaceAll((key,value)->value << 1);

查找元素

// 1.返回到指定鍵所映射的值map.get('精靈王');// 2. 返回指定鍵映射到的值，如果此映射不包含該鍵的映射，則返回給定的默認值。map.getOrDefault('精靈王','jinglingwang.cn');// 指定搜素函數// 1.通過在每個（鍵，值）上應用給定的搜索函數返回非空結果，如果沒有則返回null。 // 成功后，進一步的元素處理被抑制，并且搜索功能的任何其他并行調用的結果被忽略。Object a = map.search(5,(key,value)->{ return (value & 1) == 0 ? value : null; // 查找第一個偶數，如果是奇數返回null});// 2. 每個鍵上應用給定搜索函數的非null結果，如果沒有則返回null。String k = map.searchKeys(5,(key)->{ return 'jinglingwang'.equals(key) ? key : null;});System.out.println(k);// 3. 對每個值應用給定的搜索函數，如果沒有，返回null。Integer v2 = map.searchValues(5,(value)->{ return value == 2 ? 520 : null;});System.out.println(v2);// 4.從每個entry應用給定的搜索函數，如果沒有，則返回null。Integer a = map.searchEntries(5,(entry)->{ System.out.println('entry:'+entry.getKey() + ' ' + entry.getValue()); return 'jinglingwang.cn'.equals(entry.getKey()) ? 1 : null;});System.out.println(a);

包含

// 1. 驗證值是否存在, 等同于map.containsValue()方法map.contains(4)// 2. 驗證key是否存在map.containsKey('精靈王')// 3. 驗證值是否存在,等同于map.contains()方法map.containsValue(4)

遍歷

// 1.返回此表中鍵的枚舉map.keys();// 2.返回此地圖中包含的鍵的Set視圖map.keySet();// 3.返回此地圖中鍵的Set視圖，使用給定的映射值map.keySet(100)// 4. 返回此表中值的枚舉。map.elements();// 5.返回此地圖中包含的映射的Set視圖。map.entrySet().forEach((entry)->{ System.out.println(entry.getKey() + ' ' + entry.getValue());});// 6.1 同時遍歷key，valuemap.forEach((key,value)->{ System.out.println(key+ ' ' + value);});// 6.2 同時遍歷key，value,找到滿足條件的執行響應函數map.forEach(5,(key,value)->{ System.out.println(key+ ' ' + value); return (value & 1) == 0 ? 'jinglingwang.cn' : null;},aa->{ System.out.println(aa); // 條件中有偶數，每次就輸出jinglingwang.cn});// 7.1遍歷map.forEachEntry(5,(entry)->{ System.out.println(entry.getKey() + ' ' + entry.getValue());});// 7.2遍歷查找，滿足條件執行響應的函數map.forEachEntry(5,(entry)->{ System.out.println(entry.getKey() + ' ' + entry.getValue()); return (value & 1) == 0 ? 'jinglingwang.cn' : null;},aa->{ System.out.println(aa); // 條件中有偶數，每次就輸出jinglingwang.cn});// 8.1遍歷keymap.forEachKey(5,key->{ System.out.println('key: ' + key);});// 8.2遍歷key,滿足條件的key執行響應的函數map.forEachKey(5,key->{ System.out.println('key: ' + key); return !key.equals('jinglingwang') ? 'jinglingwang.cn' : null;},kk ->{ System.out.println(kk);});// 9.1 遍歷valuemap.forEachValue(5,value->{ System.out.println('value: ' + value);});// 9.2 遍歷value,滿足條件的value執行響應的函數map.forEachValue(5,value->{ System.out.println('value: ' + value); return (value & 1) == 0 ? 'jinglingwang.cn' : null;},vv ->{ System.out.println(vv);});reduce歸約

reduce()

//新增元素map.put('1',0);map.put('2',4);map.put('3',6);map.put('4',8);// 1. 返回使用給定的reducer組合值來累積所有（鍵，值）對的給定轉換的結果，如果沒有，則返回nullString res = map.reduce(5,(key,value)->{ System.out.println('transformer key:'+key+' value:'+value); return value+'';},(key,value)->{ System.out.println('reducer key:'+key+' value:'+value); return key+value+'';});System.out.println('res:'+res);

以上示例輸出如下：

transformer key:1 value:0transformer key:2 value:4reducer key:0 value:4transformer key:3 value:6reducer key:04 value:6transformer key:4 value:8reducer key:046 value:8res:0468

第一個transformer函數遍歷整個map，然后將返回值傳遞到reduce函數進行計算，之后reduce函數的返回值再次參與到下一次的reduce函數的計算中。

reduceToDouble()

double reduceToDouble = map.reduceToDouble(5,(key,value)->{ System.out.println('transformer key:'+key); return value;},100,(key,value)->{ System.out.println('reducer key:'+key+' value:'+value); return key+value;});System.out.println('reduceToDouble:'+reduceToDouble);// 輸出結果transformer key:1 value:0reducer key:100.0 value:0.0transformer key:2 value:4reducer key:100.0 value:4.0transformer key:3 value:6reducer key:104.0 value:6.0transformer key:4 value:8reducer key:110.0 value:8.0reduceToDouble:118.0

遍歷歸約所有的鍵值對，并把結果轉換成double類型。

類似的方法還有reduceToInt()和reduceToLong()。

reduceEntries()

// 第一種，返回值為entryMap.Entry reduceEntries = map.reduceEntries(5,entry->{ System.out.println('transformer key:'+entry.getKey()+' value:'+entry.getValue()); return entry;},(key,value)->{ System.out.println('reducer key:'+key+' value:'+value); return value;});System.out.println('reduceEntries:'+reduceEntries);// 輸出如下transformer key:1 value:0transformer key:2 value:4reducer key:1=0 value:2=4transformer key:3 value:6reducer key:2=4 value:3=6transformer key:4 value:8reducer key:3=6 value:4=8reduceEntries:4=8// 第二種String reduceEntries2 = map.reduceEntries(5,(entry)->{ System.out.println('transformer key:'+entry.getKey()+' value:'+entry.getValue()); return entry.getValue()+'';},(key,value)->{ System.out.println('reducer key:'+key+' value:'+value); return key+value+'';});System.out.println('reduceEntries2:'+reduceEntries2);transformer key:1 value:0transformer key:2 value:4reducer key:0 value:4transformer key:3 value:6reducer key:04 value:6transformer key:4 value:8reducer key:046 value:8reduceEntries2:0468

transformer 函數每次返回的是一個entry，然后會傳入到reduce函數中，reduce的return值會繼續傳遞到下一次的reduce計算。

reduceEntriesToDouble()

// 返回使用給定的reducer累加給定變換的結果，以組合值，給定基礎作為一個標識值Double reduceEntriesToDouble = map.reduceEntriesToDouble(5,entry->{ System.out.println('transformer key:'+entry.getKey()+' value:'+entry.getValue()); return Double.valueOf(entry.getValue());},100,(l,r)->{ System.out.println('reducer key:'+l+' value:'+r); return l+r;});System.out.println('reduceEntriesToDouble:'+reduceEntriesToDouble);// 輸出結果transformer key:1 value:0reducer key:100.0 value:0.0transformer key:2 value:4reducer key:100.0 value:4.0transformer key:3 value:6reducer key:104.0 value:6.0transformer key:4 value:8reducer key:110.0 value:8.0reduceEntriesToDouble:118.0

其中transformer函數是以entry的形式來進行遍歷的，第三個參數是一個歸約的標識（初始默認值），功能和reduceEntriesToInt()和reduceEntriesToLong()兩個方法非常相似。

reduceKeys()

// 1.第一種，只有reduce函數，遍歷所有的鍵值對，reduce函數的返回值會作為下一次的key，如果沒有則返回null。String newKey = map.reduceKeys(5,(key,value)->{ System.out.println('reducer key:'+key+' value:'+value); return key+value;**}**);System.out.println('newKey:'+newKey);// 輸出結果reducer key:1 value:2reducer key:12 value:3reducer key:123 value:4newKey:1234// 2.第二種，有transformer和reducer String newValue = map.reduceKeys(5,(key)->{ System.out.println('transformer key:'+key); return key;},(key,value)->{ System.out.println('reducer key:'+key+' value:'+value); return key+value;});System.out.println('newValue:'+newValue);// 輸出結果transformer key:1transformer key:2reducer key:1 value:2transformer key:3reducer key:12 value:3transformer key:4reducer key:123 value:4newValue:1234

reduceKeysToDouble()

double reduceKeysToDouble = map.reduceKeysToDouble(5,(key)->{ System.out.println('transformer key:'+key); return Double.parseDouble(key);},100,(key,value)->{ System.out.println('reducer key:'+key+' value:'+value); return key+value;});System.out.println('reduceKeysToDouble:'+reduceKeysToDouble);

遍歷歸約所有的key，并把結果轉換成double類型。

類似的方法還有reduceKeysToInt()和reduceKeysToLong()。

reduceValues()

// 第一種：僅reducer函數double reduceValues = map.reduceValues(5,(key,value)->{ System.out.println('reducer key:'+key+' value:'+value); return key+value;});System.out.println('reduceValues:'+reduceValues);//輸出結果reducer key:0 value:4reducer key:4 value:6reducer key:10 value:8reduceValues:18.0// 第二種，含有transformerdouble reduceValues2 = map.reduceValues(5,(value)->{ System.out.println('transformer value:'+value); return Double.valueOf(value);},(key,value)->{ System.out.println('reducer key:'+key+' value:'+value); return key+value;});System.out.println('reduceValues2:'+reduceValues2);// 輸出結果transformer value:0transformer value:4reducer key:0.0 value:4.0transformer value:6reducer key:4.0 value:6.0transformer value:8reducer key:10.0 value:8.0reduceValues2:18.0

reduceValuesToDouble()

double reduceValuesToDouble = map.reduceValuesToDouble(5,(value)->{ System.out.println('transformer value:'+value); return Double.valueOf(value);},100,(l,r)->{ System.out.println('reducer key:'+l+' value:'+r); return l+r;});System.out.println('reduceValuesToDouble:'+reduceValuesToDouble);// 輸出結果transformer value:0reducer key:100.0 value:0.0transformer value:4reducer key:100.0 value:4.0transformer value:6reducer key:104.0 value:6.0transformer value:8reducer key:110.0 value:8.0reduceValuesToDouble:118.0

遍歷歸約所有的value，并把結果轉換成double類型。

類似的方法還有reduceValuesToInt()和reduceValuesToLong()。

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