Introduction to ConcurrentHashMap in Java

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ConcurrentHashMap is a subclass of HashMap and is designed for use in multi-threaded environments. It maintains a configurable concurrency stage (default worth of 16), which could be specified whereas creating the map. The upper the concurrency stage, the extra threads can entry its buckets without delay, however this can lead to extra competition if all getEnumerators() will not be synchronized appropriately. This Java programming tutorial discusses ConcurrentHashMap in Java with code examples wherever applicable.

To be taught extra about hashing, try our tutorial: Introduction to Hashing in Java.

What Is ConcurrentHashMap in Java?

In Java, a ConcurrentHashMap is a knowledge construction used for storing and retrieving information in a concurrent method. This information construction is designed for use in multi-threaded functions the place a number of threads are studying and writing to the hash map concurrently.

ConcurrentHashMap is a Java class that allows a number of threads to entry the map on the identical level of time. It is part of the Java Collections Framework, and it offers a means for functions to effectively deal with concurrent updates to the map.

The ConcurrentHashMap class offers a number of strategies for doing fundamental operations on the map, comparable to placing values into the map and getting values out of the map. Moreover, the category offers a number of strategies for doing extra superior operations, comparable to iterating over the key-value pairs within the map or retrieving a set of keys which can be related to a given worth.

Why Ought to Builders Use ConcurrentHashMap?

The ConcurrentHashMap is a strong information construction that allows Java builders to work with concurrent information in a secure and environment friendly method. The ConcurrentHashMap offers a variety of options that makes it effectively fitted to working with concurrent information, together with:

  • Atomic operations: All operations on the ConcurrentHashMap are atomic, which suggests you possibly can safely carry out concurrent information entry.
  • Lock-free: The ConcurrentHashMap is designed to be lock-free, which implies that there isn’t any want to accumulate a lock to be able to learn or write information. This makes the ConcurrentHashMap very environment friendly when utilized in a multi-threaded atmosphere.
  • Scalable: The ConcurrentHashMap is designed to be scalable, which suggests it will possibly effectively deal with massive quantities of information.

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How Does ConcurrentHashMap Work in Java?

ConcurrentHashMap is a strong information construction that allows quick, thread-safe operations on information. The map works by permitting every thread to securely entry and modify the info with out having to fret about different threads interfering. That is completed by utilizing a particular locking mechanism that solely permits one thread to entry the info at a time.

This locking mechanism known as a segmented lock. It really works by dividing the info into small segments, after which permitting every thread to lock one phase at a time. This manner, a number of threads can work on the info concurrently, however they are going to by no means be engaged on the identical information on the identical time.

The segmented lock is applied utilizing a particular Java class known as ReentrantLock. ReentrantLock is a strong synchronization device that enables threads to securely lock information constructions. It’s utilized by many Java courses, together with ConcurrentHashMap.

The ReentrantLock class has two predominant strategies: lock() and unlock(). When a thread calls lock(), it can try to accumulate the lock for the info construction. If the lock is accessible, the thread will purchase it and may then safely entry and modify the info.

Within the absence of a lock, the thread will wait till one other thread releases it. As soon as the thread has acquired the lock, it will possibly execute the essential part code after which launch it by calling the unlock() technique.

The ReentrantLock class additionally has a tryLock() technique, which permits a thread to try to accumulate the lock with out ready. This may be helpful in conditions the place you do not need to dam different threads if the lock isn’t obtainable.

Methods to Program ConcurrentHashMap in Java

The ConcurrentHashMap class extends from the HashMap class and it’s applied to assist concurrent entry. It is usually thread-safe, which implies that a number of threads can entry it with none points. To create a ConcurrentHashMap, you possibly can write the next Java code:

ConcurrentHashMap concurrentHashMap = new ConcurrentHashMap();  

The next code itemizing can be utilized to retailer gadgets in a ConcurrentHashMap after which show them on the console window:

import java.util.concurrent.*;
class MyConcurrentHashMap {
 public static void predominant(String[] args)
        ConcurrentHashMap<String, String> concurrentHashMap
            = new ConcurrentHashMap<>();
        concurrentHashMap.put("P001", "Lenovo Legion");
        concurrentHashMap.put("P002", "DELL Inspiron");
        concurrentHashMap.put("P003", "Lenovo ThinkPad");

When to Use ConcurrentHashMap in Java?

When a number of threads entry a knowledge construction on the identical level of time, it will possibly result in unpredictable outcomes and even deadlocks. Because of this if you will implement your individual model, it’s essential to make it possible for it’s thread-safe by utilizing synchronization primitives comparable to locks or semaphores.

ConcurrentHashMap is a superb selection for high-performance functions, because it presents quick lookup and insertion instances. It presents a number of options that make it well-suited for such a atmosphere, together with the flexibility to lock and unlock particular person buckets, in addition to to atomically add and take away parts.

Mainly, you must use it everytime you want a concurrent map that doesn’t block when used. For instance, when you’re working with a number of thread-safe information, or if it’s essential to entry the map from a number of threads, ConcurrentHashMap is an efficient possibility. It’s additionally a good selection if it’s essential to retailer a considerable amount of information and wish it to be accessible from a number of threads.

The ConcurrentHashMap is designed to be accessed by a number of threads for studying or writing information. You possibly can entry it from a number of threads with out locking your complete object so that you don’t have to attend when one thread locks one other a part of your program whereas accessing it.

ConcurrentHashMap additionally helps atomic putIfAbsent() and get() operations which lets you lock solely that merchandise if it exists to be able to add new information or retrieve present information from map respectively with none deadlocks if different threads are already operating these operations on another entry inside this map.

When utilizing a Hashtable or synchronized assortment, your complete assortment is locked throughout reads and writes. With a ConcurrentHashMap, solely the required factor is locked for studying or writing. This permits for higher efficiency as a result of a couple of thread can learn information without delay.

Don’t use it when you want sequential entry to parts within the map. A concurrent map doesn’t assure that an merchandise might be obtainable instantly after one other merchandise has been modified; there may very well be different threads modifying completely different components of it at any given time time limit which means that there isn’t any assured ordering after modifications.

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ConcurrentHashMap vs HashMap in Java

In the beginning, the ConcurrentHashMap class is designed to be used in concurrent information entry, whereas the Hashtable class isn’t. Because of this the ConcurrentHashMap class could be safely utilized by a number of threads concurrently, with out the chance of information corruption or race situations.

Second, the ConcurrentHashMap class is far more environment friendly than the Hashtable class. It makes use of a hash-based algorithm to retailer and retrieve information, which makes it sooner and extra scalable. Lastly, the ConcurrentHashMap class presents a variety of highly effective options that aren’t obtainable within the Hashtable class. These embrace assist for locking, evicting and iterating over entries, and including and eradicating entries from the map.

There are just a few completely different situations wherein it is sensible to make use of a ConcurrentHashMap over a daily HashMap. One widespread situation is when it’s essential to assist a number of readers and writers concurrently. This may very well be the case in an online utility, for instance, the place a number of customers are accessing information on the identical time.

One other situation wherein ConcurrentHashMap is helpful is when it’s essential to carry out frequent reads and rare writes. On this case, it may be extra environment friendly to make use of a ConcurrentHashMap as a result of writes won’t block reads.

ConcurrentHashMap is good for high-performance, multi-threaded functions. If it’s essential to entry and replace a map from a number of threads, ConcurrentHashMap is the best choice. It offers all of the operations of a HashMap and moreover permits concurrent entry for learn, write, and replace.

ConcurrentHashMap vs Hashtable in Java

ConcurrentHashMap makes use of a number of locks, so completely different components of the map could be up to date concurrently with out blocking one another. Hashtable, however, makes use of a single lock for your complete map, which may result in efficiency points. Nonetheless, not like Hashtable, accesses to ConcurrentHashMap are typically not blocked when a lock is unavailable. This permits for a lot increased concurrency in retrieving information from a ConcurrentHashMap.

When updating a ConcurrentHashMap, a number of threads can lock completely different parts of the map for updates. The variety of locks is configurable at creation time, and could be adjusted if wanted.

Locking a portion of the map solely blocks different threads from updating the locked portion; it doesn’t block different threads from studying different components of the map that aren’t locked. In contrast to a Hashtable, null keys and values will not be allowed in a ConcurrentHashMap.

When To not use ConcurrentHashMap in Java

ConcurrentHashMap isn’t a good selection when you would wish to take care of insertion order of the weather. It is because the inner construction of a ConcurrentHashMap relies on hash codes, which implies that the order wherein parts are inserted isn’t preserved.

One other scenario wherein it isn’t ideally suited to make use of a ConcurrentHashMap is when it’s essential to synchronize entry to your complete map. It is because every phase of the map is locked independently, so locking your complete map would require locking every phase individually, which might be inefficient.

Ultimate Ideas on ConcurrentHashMap in Java

ConcurrentHashMap is a Java class that enables a number of threads to entry the map concurrently. It is part of the Java Collections Framework, and it offers a means for functions to effectively deal with concurrent updates to the map. ConcurrentHashMap is completely different from conventional HashMap in that it makes use of a lock to make sure that just one thread can modify the map at a time. This prevents information corruption and race situations.

ConcurrentHashMap is an extension of the Map interface that may maintain a number of entries on the identical time. You possibly can benefit from ConcurrentHashMap to carry out concurrent updates on its assortment of keys, and values with out locking out readers or writers for any vital time frame. The important thing options of ConcurrentHashMap are: efficiency, scalability and thread security, that are essential for concurrent programming.

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