Which are concurrent collections in Java?

Which are concurrent collections in Java?

I'd be happy to help you with that!

Concurrent collections in Java refer to the data structures and classes provided by the Java Collections Framework (JCF) that enable safe and efficient manipulation of shared resources, such as lists, sets, maps, and queues, while multiple threads access and modify them concurrently. In other words, concurrent collections are designed to handle the challenges of multithreaded programming in Java.

Here are some of the most important concurrent collections in Java:

When choosing a concurrent collection in Java, consider the following factors:

In summary, Java provides a range of concurrent collections that can help developers write more robust and scalable code for multithreaded applications. By understanding the characteristics and trade-offs between these classes, you'll be better equipped to choose the best one for your specific needs.

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Java concurrent collections list example

I'm happy to provide an example of using the java.util.concurrent package, specifically the ConcurrentHashMap and CopyOnWriteArrayList, in a concurrent programming scenario.

Let's consider a simple banking system where multiple threads need to access and update account balances concurrently. We'll use ConcurrentHashMap to store customer accounts with their balances and CopyOnWriteArrayList to keep track of transaction history.

Here's an example code:

import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.locks.ReentrantLock;
class BankAccount {
private int balance;
private ConcurrentHashMap<String, Integer> transactions = new ConcurrentHashMap<>();
public BankAccount(int initialBalance) {
balance = initialBalance;
}
public void deposit(String customerName, int amount) {
balance += amount;
transactions.put(customerName, balance);
}
public void withdraw(String customerName, int amount) {
if (balance >= amount) {
balance -= amount;
transactions.put(customerName, balance);
} else {
System.out.println("Insufficient funds!");
}
}
}
class TransactionThread extends Thread {
private BankAccount account;
private CopyOnWriteArrayList history = new CopyOnWriteArrayList<>();
public TransactionThread(BankAccount account) {
this.account = account;
}
@Override
public void run() {
for (int i = 0; i < 10; i++) { // simulate multiple transactions
int amount = (int) (Math.random() * 100); // random transaction amount
if (Math.random() > 0.5) { // 50% chance of deposit or withdrawal
account.deposit("Customer " + Thread.currentThread().getName(), amount);
} else {
account.withdraw("Customer " + Thread.currentThread().getName(), amount);
}
history.add(new Transaction(Thread.currentThread().getName(), amount));
}
}
}
class Transaction {
private String customer;
private int amount;
public Transaction(String customer, int amount) {
this.customer = customer;
this.amount = amount;
}
@Override
public String toString() {
return "Transaction{" +
"customer='" + customer + ''' +
", amount=" + amount +
'}';
}
}
public class ConcurrentBankingExample {
public static void main(String[] args) throws InterruptedException {
BankAccount account = new BankAccount(1000);
Thread[] threads = new Thread[5]; // create 5 threads
for (int i = 0; i < 5; i++) {
TransactionThread thread = new TransactionThread(account);
threads[i] = thread;
thread.start();
}
// wait for all transactions to complete
for (Thread t : threads) {
t.join();
}
System.out.println("Final account balance: " + account.balance);
CopyOnWriteArrayList transactionHistory = new CopyOnWriteArrayList<>();
account.transactions.forEach((customer, amount) -> {
transactionHistory.add(new Transaction(customer, amount));
});
System.out.println("Transaction History:");
for (Transaction t : transactionHistory) {
System.out.println(t);
}
}
}

In this example:

Multiple threads are created, each simulating multiple transactions (deposits or withdrawals). Each thread updates the account balance using the ConcurrentHashMap.

After all transactions have been completed, we print the final account balance and transaction history.

This example demonstrates how java.util.concurrent classes can be used to write concurrent code that is safe, efficient, and easy to understand.