Java ConcurrentHashMap的使用示例

 // 1.无参数构造方法 new ConcurrentHashMap(); // 2.指定初始容量 new ConcurrentHashMap(initialCapacity) // 3.指定初始容量和加载因子 new ConcurrentHashMap(initialCapacity,loadFactor) // 4.指定初始容量和加载因子与并发级别(并发更新线程数) new ConcurrentHashMap(initialCapacity, loadFactor, concurrencyLevel) // 5.创建与给定映射具有相同映射的新映射 new ConcurrentHashMap(Map m)

 // 1.添加元素，不允许null map.put(1,1); // 2.添加一个map map.putAll(map); // 3.添加元素, 键不存在映射关系才添加成功 map.putIfAbsent(2,1);

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

 // 1.替换指定key map.replace(1,3); // 2.替换指定key,value map.replace(1,2,4); // 3.替换所有，这里是把value都乘以2 map.replaceAll((key,value)->value << 1);

 // 1.返回到指定键所映射的值 map.get("精灵王"); // 2. 返回指定键映射到的值，如果此映射不包含该键的映射，则返回给定的默认值。 map.getOrDefault("精灵王","jinglingwang.cn"); // 指定搜素函数 // 1.通过在每个（键，值）上应用给定的搜索函数返回非空结果，如果没有则返回null。 //   成功后，进一步的元素处理被抑制，并且搜索功能的任何其他并行调用的结果被忽略。 Object a = map.search(5,(key,value)->{ return (value & 1) == 0 ? value : null; // 查找第一个偶数，如果是奇数返回null }); // 2. 每个键上应用给定搜索函数的非null结果，如果没有则返回null。 String k = map.searchKeys(5,(key)->{ return "jinglingwang".equals(key) ? key : null; }); System.out.println(k); // 3. 对每个值应用给定的搜索函数，如果没有，返回null。 Integer v2 = map.searchValues(5,(value)->{ return value == 2 ? 520 : null; }); System.out.println(v2); // 4.从每个entry应用给定的搜索函数，如果没有，则返回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);

 // 1. 验证值是否存在, 等同于map.containsValue()方法 map.contains(4) // 2. 验证key是否存在 map.containsKey("精灵王") // 3. 验证值是否存在,等同于map.contains()方法 map.containsValue(4)

 // 1.返回此表中键的枚举 map.keys(); // 2.返回此地图中包含的键的Set视图 map.keySet(); // 3.返回此地图中键的Set视图，使用给定的映射值 map.keySet(100) // 4. 返回此表中值的枚举。 map.elements(); // 5.返回此地图中包含的映射的Set视图。 map.entrySet().forEach((entry)->{ System.out.println(entry.getKey() + " " + entry.getValue()); }); // 6.1 同时遍历key，value map.forEach((key,value)->{ System.out.println(key+ " " + value); }); // 6.2 同时遍历key，value,找到满足条件的执行响应函数 map.forEach(5,(key,value)->{ System.out.println(key+ " " + value); return (value & 1) == 0 ? "jinglingwang.cn" : null; },aa->{ System.out.println(aa); // 条件中有偶数，每次就输出jinglingwang.cn }); // 7.1遍历 map.forEachEntry(5,(entry)->{ System.out.println(entry.getKey() + " " + entry.getValue()); }); // 7.2遍历查找，满足条件执行响应的函数 map.forEachEntry(5,(entry)->{ System.out.println(entry.getKey() + " " + entry.getValue()); return (value & 1) == 0 ? "jinglingwang.cn" : null; },aa->{ System.out.println(aa); // 条件中有偶数，每次就输出jinglingwang.cn }); // 8.1遍历key map.forEachKey(5,key->{ System.out.println("key: " + key); }); // 8.2遍历key,满足条件的key执行响应的函数 map.forEachKey(5,key->{ System.out.println("key: " + key); return !key.equals("jinglingwang") ? "jinglingwang.cn" : null; },kk ->{ System.out.println(kk); }); // 9.1 遍历value map.forEachValue(5,value->{ System.out.println("value: " + value); }); // 9.2 遍历value,满足条件的value执行响应的函数 map.forEachValue(5,value->{ System.out.println("value: " + value); return (value & 1) == 0 ? "jinglingwang.cn" : null; },vv ->{ System.out.println(vv); });

 //新增元素 map.put("1",0); map.put("2",4); map.put("3",6); map.put("4",8); // 1. 返回使用给定的reducer组合值来累积所有（键，值）对的给定转换的结果，如果没有，则返回null String 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);

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

 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); // 输出结果 transformer key:1 value:0 reducer key:100.0 value:0.0 transformer key:2 value:4 reducer key:100.0 value:4.0 transformer key:3 value:6 reducer key:104.0 value:6.0 transformer key:4 value:8 reducer key:110.0 value:8.0 reduceToDouble:118.0

 // 第一种，返回值为entry Map.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); // 输出如下 transformer key:1 value:0 transformer key:2 value:4 reducer key:1=0 value:2=4 transformer key:3 value:6 reducer key:2=4 value:3=6 transformer key:4 value:8 reducer key:3=6 value:4=8 reduceEntries:4=8 // 第二种 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:0 transformer key:2 value:4 reducer key:0 value:4 transformer key:3 value:6 reducer key:04 value:6 transformer key:4 value:8 reducer key:046 value:8 reduceEntries2:0468

 // 返回使用给定的reducer累加给定变换的结果，以组合值，给定基础作为一个标识值 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); // 输出结果 transformer key:1 value:0 reducer key:100.0 value:0.0 transformer key:2 value:4 reducer key:100.0 value:4.0 transformer key:3 value:6 reducer key:104.0 value:6.0 transformer key:4 value:8 reducer key:110.0 value:8.0 reduceEntriesToDouble:118.0

 // 1.第一种，只有reduce函数，遍历所有的键值对，reduce函数的返回值会作为下一次的key，如果没有则返回null。 String newKey = map.reduceKeys(5,(key,value)->{ System.out.println("reducer key:"+key+" value:"+value); return key+value; **}**); System.out.println("newKey:"+newKey); // 输出结果 reducer key:1 value:2 reducer key:12 value:3 reducer key:123 value:4 newKey:1234 // 2.第二种，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); // 输出结果 transformer key:1 transformer key:2 reducer key:1 value:2 transformer key:3 reducer key:12 value:3 transformer key:4 reducer key:123 value:4 newValue:1234

 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);

 // 第一种：仅reducer函数 double reduceValues = map.reduceValues(5,(key,value)->{ System.out.println("reducer key:"+key+" value:<strong style="color:transparent">来源gaodai#ma#com搞@代~码网</strong>"+value); return key+value; }); System.out.println("reduceValues:"+reduceValues); //输出结果 reducer key:0 value:4 reducer key:4 value:6 reducer key:10 value:8 reduceValues:18.0 // 第二种，含有transformer double 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); // 输出结果 transformer value:0 transformer value:4 reducer key:0.0 value:4.0 transformer value:6 reducer key:4.0 value:6.0 transformer value:8 reducer key:10.0 value:8.0 reduceValues2:18.0

 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); // 输出结果 transformer value:0 reducer key:100.0 value:0.0 transformer value:4 reducer key:100.0 value:4.0 transformer value:6 reducer key:104.0 value:6.0 transformer value:8 reducer key:110.0 value:8.0 reduceValuesToDouble:118.0