Can we make HashMap synchronized?

HashMap can be synchronized using the Collections. synchronizedMap() method. The synchronizedMap() method of java.

How do you make a HashMap synchronized?

According to Oracle docs, in order to synchronize HashMap we need to use Collections. synchronizedMap(hashmap). It returns a thread safe map backed up by the specified HashMap. Other important point to note that iterator should be used in a synchronized block even if we have synchronized the HashMap explicitly.

Is HashMap synchronized or not?

HashMap is non-synchronized. It is not thread-safe and can't be shared between many threads without proper synchronization code whereas Hashtable is synchronized. It is thread-safe and can be shared with many threads.

Is HashMap synchronized by default?

Java HashMap is not synchronized by default.

How is hash table synchronized?

Hashtable is synchronized. It ensures that no more than one thread can access the Hashtable at a given moment of time. The thread which works on Hashtable acquires a lock on it to make the other threads wait till its work gets completed. 2) HashMap allows one null key and any number of null values.

#12 - Difference b/w ConcurrentHashMap

Is HashSet synchronized?

1) Both HashMap and HashSet are not synchronized which means they are not suitable for thread-safe operations unitl unless synchronized explicitly. This is how you can synchronize them explicitly: HashSet: Set s = Collections.

Why HashMap is faster than Hashtable?

HashMap is not synchronized, therefore it's faster and uses less memory than Hashtable. Generally, unsynchronized objects are faster than synchronized ones in a single threaded application.

Why is synchronized HashMap better than ConcurrentHashMap?

ConcurrentHashMap allows performing concurrent read and write operation. Hence, performance is relatively better than the Synchronized Map. In Synchronized HashMap, multiple threads can not access the map concurrently. Hence, the performance is relatively less than the ConcurrentHashMap.

Why HashMap is not thread-safe in Java?

Well, HashMap is not thread-safe. If multiple threads are accessing the same HashMap object and try to modify the structure of the HashMap (using put() or remove() method), it may cause an inconsistency in the state of HashMap .

Is synchronized HashMap thread-safe?

synchronizedMap() and ConcurrentHashMap both provide thread-safe operations on collections of data.

Is HashMap faster than ConcurrentHashMap?

The summary

If you choose a single thread access use HashMap , it is simply faster. For add method it is even as much as 3x more efficient. Only get is faster on ConcurrentHashMap , but not much.

Can HashMap have duplicate keys?

HashMap stores key, value pairs and it does not allow duplicate keys. If the key is duplicate then the old key is replaced with the new value.

Is HashMap thread-safe for read only?

As long as no thread is modifying the map (adding or removing a key/value pair, or mutating an existing value) while other threads are reading then it is thread-safe.

Can we make HashMap thread-safe?

You can make HashMap thread safe by wrapping it with Collections. synchronizedMap() .

Why do we need ConcurrentHashMap?

You should use ConcurrentHashMap when you need very high concurrency in your project. It is thread safe without synchronizing the whole map . Reads can happen very fast while write is done with a lock. There is no locking at the object level.

Why HashMap should not be used in multithreaded environment?

HashMap allows multiple threads to operate simultaneously. Therefore, there are chances of data-insistency when multiple threads are performing some operation on HashMap . Hence HashMap is not preferable (not thread-safe) in a multi-threaded environment.

Is HashMap immutable?

yes because it is unchangeable. Show activity on this post. If you object is immutable and implements hashcode/equals correctly, you are fine to use them as keys in a hashmap.

Is ConcurrentHashMap slower than HashMap?

Only modifying operations on ConcurrentHashMap are synchronized. Hence, add or remove operations on ConcurrentHashMap are slower than on HashMap . The read operations on both, ConcurrentHashMap and HashMap , give same performance as read operations on both maps are not synchronized.

Can HashMap have null key?

Hashtable does not allow null keys or values, while HashMap allows null values and 1 null key.

Is TreeMap synchronized?

The implementation of a TreeMap is not synchronized. This means that if multiple threads access a tree set concurrently, and at least one of the threads modifies the set, it must be synchronized externally. This is typically accomplished by using the Collections.

What is difference between HashMap and synchronized HashMap?

2) Which operations are synchronized? In synchronized HashMap and HashTable , all operations are synchronized. That means, whatever the operation you want to perform on the map, whether it is read or update, you have to acquire object lock. But in ConcurrentHashMap , only update operations are synchronized.

How null key is stored in HashMap?

In Hashmap one null key is allowed and multiple null values are allowed. Since hashcode of null is 0 so null key actually stored at index 0 in hashmap. Hashmap in java actsually created as Array of linkedlist where index in array is find out by hashing on key.

Can we create custom object in HashMap?

Answer to your question is yes, objects of custom classes can be used as a key in a HashMap.

Is Hashtable same as Map?

Though both Hashtable and HashMap are data-structure based upon hashing and implementation of Map interface, the main difference between them is that HashMap is not thread-safe but Hashtable is thread-safe. This means you cannot use HashMap in a multi-threaded Java application without external synchronization.

Is LinkedList synchronized?

LinkedList maintains insertion order of the elements. Java LinkedList Class is not synchronized, that means in a multi-threaded environment you must synchronize concurrent modifications to the linked list externally. We can use Collections. synchronizedList(new LinkedList()) to get synchronized linked list.