在Java语言中,给ConcurrentHashMap和Hashtable这些线程安全的集合中的Key或者Value插入 null(空) 值的会报空指针异常,但是单线程操作的HashMap又允许 Key 或者 Value 插入 null(空) 值。这到底是为什么呢? 1、探寻源码 为了找到原因,我们先来看这样一段源码片段,打开ConcurrentHashMap的pu
Java 8对ConcurrentHashMap的实现进一步做了优化。首先，与HashMap的改进类似，在哈希冲突比较严重的时候，...
在Java 语言中,HashMap 这种单线程下使用的集合是可以设置 null 值的,而并发集合如 ConcurrentHashMap 或 Hashtable 是不允许给 key 或 value 设置 null 值的,这是 JDK 源码层面直接实现的,这样设计的目的主要是为了防止并发场景下的歧义问题。
对于ConcurrentHashMap来说，它也不允许存储键值对为null的数据。 Doug Lea（ConcurrentHashMap的设计者）...
and replace all use of nulls in uses of maps with NULL? -Doug 以上信件的主要意思是,Doug Lea 认为这样设计最主要的原因是:不容忍在并发场景下出现歧义! 总结 在Java 语言中,HashMap 这种单线程下使用的集合是可以设置 null 值的,而并发集合如 ConcurrentHashMap 或 Hashtable 是不允许给 key 或 ...
However, even though all operations are thread-safe, retrieval operations do not entail locking, and there is not any support for locking the entire table in a way that prevents all access. This class is fully interoperable with Hashtable in programs that rely on its thread safety but not ...
In a non-concurrent map, you can check this via map.contains(key),but in a concurrent one, the map might have changed between calls. Further digressing: I personally think that allowing nulls in Maps (also Sets) is an open invitation for programs ...
在Java 语言中,HashMap 这种单线程下使用的集合是可以设置 null 值的,而并发集合如 ConcurrentHashMap 或 Hashtable 是不允许给 key 或 value 设置 null 值的,这是 JDK 源码层面直接实现的,这样设计的目的主要是为了防止并发场景下的歧义问题。 参考文档 ...
Learn to create clone of a HashMap in Java. We will see the java programs to create shallow copy and deep copy of a HashMap. 1. Creating a Shallow Copy of Map We can create a shallow copy of a given HashMap in two ways. The first uses … ...
In a non-concurrent map, you can check this via map.contains(key),but in a concurrent one, the map might have changed between calls. Further digressing: I personally think that allowing nulls in Maps (also Sets) is an open invitation for programs to contain errors that remain undetected ...