Java ConcurrentHashMap是什么

说明

1、ConcurentHashMap结合了HashMap和Hashtable的优点。HashMap不考虑同步，Hashtable考虑同步。但是Hashtable每次同步都要锁定整个结构。

2、ConcurentHashMap锁的方式是稍微细粒度的。ConcurentHashMap将hash表分成16桶(默认值)，如get、put、remove等常用操作只锁定目前需要的桶。

实例

/**
     * Creates a new, empty map with the default initial table size (16).
     */
    public ConcurrentHashMap() {
    }
 
    /**
     * Creates a new, empty map with an initial table size
     * accommodating the specified number of elements without the need
     * to dynamically resize.
     *
     * @param initialCapacity The implementation performs internal
     * sizing to accommodate this many elements.
     * @throws IllegalArgumentException if the initial capacity of
     * elements is negative
     */
    public ConcurrentHashMap(int initialCapacity) {
        if (initialCapacity < 0)
            throw new IllegalArgumentException();
        int cap = ((initialCapacity >= (MAXIMUM_CAPACITY >>> 1)) ?
                   MAXIMUM_CAPACITY :
                   tableSizeFor(initialCapacity + (initialCapacity >>> 1) + 1));
        this.sizeCtl = cap;
    }
 
    /**
     * Creates a new map with the same mappings as the given map.
     *
     * @param m the map
     */
    public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
        this.sizeCtl = DEFAULT_CAPACITY;
        putAll(m);
    }

以上就是Java ConcurrentHashMap的介绍，希望对大家有所帮助。更多Java学习指路：Java基础

本教程操作环境：windows7系统、java10版，DELL G3电脑。