Java并发编程之详解ConcurrentHashMap类

// 创建容量为8，负载系数为0.6的ConcurrentHashMap
ConcurrentHashMap<Key, Value> numbers = new ConcurrentHashMap<>(8, 0.6f);

ConcurrentHashMap<Key, Value> numbers1 = new ConcurrentHashMap<>();

import java.util.concurrent.ConcurrentHashMap;

class Main {
    public static void main(String[] args) {
        // 创建ConcurrentHashMap 用于保存偶数
        ConcurrentHashMap<String, Integer> evenNumbers = new ConcurrentHashMap<>();

        // 使用put()方法插入数据
        evenNumbers.put("Two", 2);
        evenNumbers.put("Four", 4);

        // 使用putIfAbsent()插入数据
        evenNumbers.putIfAbsent("Six", 6);
        System.out.println("偶数集合ConcurrentHashMap: " + evenNumbers);

        //创建ConcurrentHashMap用于保存整数
        ConcurrentHashMap<String, Integer> numbers = new ConcurrentHashMap<>();
        numbers.put("One", 1);

        // 使用putAll()插入数据
        numbers.putAll(evenNumbers);
        System.out.println("整数集合ConcurrentHashMap: " + numbers);
    }
}

偶数集合ConcurrentHashMap: {Six=6, Four=4, Two=2}
整数集合ConcurrentHashMap: {Six=6, One=1, Four=-4, Two=2}

import java.util.concurrent.ConcurrentHashMap;

class Main {
    public static void main(String[] args) {
        ConcurrentHashMap<String, Integer> numbers = new ConcurrentHashMap<>();

        numbers.put("One", 1);
        numbers.put("Two", 2);
        numbers.put("Three", 3);
        System.out.println("ConcurrentHashMap: " + numbers);

        // 获取 map中key/value 键值对集合
        System.out.println("Key/Value mappings: " + numbers.entrySet());

        // 获取map中所有的key的集合
        System.out.println("Keys: " + numbers.keySet());

        // 获取map中所有的value的集合
        System.out.println("Values: " + numbers.values());
    }
}

import java.util.concurrent.ConcurrentHashMap;

class Main {
    public static void main(String[] args) {

        ConcurrentHashMap<String, Integer> numbers = new ConcurrentHashMap<>();
        numbers.put("One", 1);
        numbers.put("Two", 2);
        numbers.put("Three", 3);
        System.out.println("ConcurrentHashMap: " + numbers);

        // 获取指定key元素的value值，如果key不存在返回null
        int value1 = numbers.get("Three");
        System.out.println("Using get(): " + value1);

        // 获取指定key元素的value值，如果key不存在返回一个指定的默认值
        int value2 = numbers.getOrDefault("Five", 5);
        System.out.println("Using getOrDefault(): " + value2);
    }
}

import java.util.concurrent.ConcurrentHashMap;

class Main {
    public static void main(String[] args) {

        ConcurrentHashMap<String, Integer> numbers = new ConcurrentHashMap<>();
        numbers.put("One", 1);
        numbers.put("Two", 2);
        numbers.put("Three", 3);
        System.out.println("ConcurrentHashMap: " + numbers);

        // 根据指定的key删除map中的元素，并将该元素返回
        int value = numbers.remove("Two");
        System.out.println("Removed value: " + value);

        // 只有当map中存在指定的键映射到指定的值时，才会从map中删除条目，并返回一个布尔值。
        boolean result = numbers.remove("Three", 3);
        System.out.println("Is the entry {Three=3} removed? " + result);

        System.out.println("Updated ConcurrentHashMap: " + numbers);
    }
}