Why Hashtable does not allow null key and value and HashMap allow one null key and multiple value?

Why Hashtable does not allow null key and value and HashMap allow one null key and multiple value?

Geek now you must be wondering why HashTable doesn’t allow null and HashMap do? The answer is simple s in order to successfully store and retrieve objects from a HashTable, the objects used as keys must implement the hashCode method and the equals method. Since null is not an object, it can’t implement these methods.

Why null key is not allowed in Hashtable and Concurrenthashmap but allowed in HashMap?

The main reason that nulls aren’t allowed in ConcurrentMaps (ConcurrentHashMaps, ConcurrentSkipListMaps) is that ambiguities that may be just barely tolerable in non-concurrent maps can’t be accommodated. The main one is that if map.

Why HashMap does allow null key?

For HashMap, it allows one null key and there is a null check for keys, if the key is null then that element will be stored in a zero location in Entry array. We cannot have more than one Null key in HashMap because Keys are unique therefor only one Null key and many Null values are allowed.

Why Hashtable doesn allow null but HashMap allow?

So HashMap can tolerate null values. However for Hashtable and ConcurrentHashMap, the expectations are clear that multiple threads are going to act on the data. Hence they cannot afford to allow null values and give out incorrect answer. Same logic goes for keys.

Why null is not allowed in TreeMap?

It contains only unique elements. It cannot have null key but can have multiple null values. It is same as HashMap instead maintains ascending order(Sorted using the natural order of its key).

What is the difference between a Hashtable and Properties?

Properties is a very specialized class that’s designed to hold configuration and/or resources that are usually stored in some file. It has several features that Hashtable doesn’t have (and shouldn’t have): It supports reading and writing its content to a well-defined plain-text format (using load() / store() )

What is ConcurrentHashMap and Hashtable in Java Why is ConcurrentHashMap considered faster than Hashtable?

Answer: ConcurrentHashMap is introduced in Java 1.5. ConcurrentHashMap uses multiple buckets to store data. This avoids read locks and greatly improves performance over a HashTable.

Can Hashtable replace ConcurrentHashMap without external synchronization?

ConcurrentHashMap was introduce with JDK1. 5 release to replace legacy class Hashtable. While ConcurrentHashMap is specially designed for concurrent uses which by default allows 16 threads to simultaneously read and write from map without any external synchronization.

Why does hashhashtable not allow null values?

HashTable – Does not allow null keys This is because, in put(K key, V value) method, we have key.hashcode() which throws null pointer exception. HashMap allows null values as it doesn’t have any checks like HashTable, while it allows only one null key.

Does HashMap allow null key and null values in Java?

JavaMadeSoEasy.com (JMSE) Yes, HashMap allows null key and null values. HashMap allows to store one null key and many null values i.e. many keys can have null value in java.

What is the difference between HashMap and hashtable in Java?

HashMap allows to store one null key and many null values i.e. many keys can have null value in java. Hashtable does not allow to store null key or value in java.

Why is put not allowed in hashtable in Java?

So, they did not allow it in the Hashtable. The put method to insert key value pair in Hashtable throws NullPointerException if value is null. Since Hashtable is based on hashing mechanism, hash is calculated for keys, which throws NullPointerException if key is null.