Java Thread Synchronization: Synchronized Blocks, Methods, and Intrinsic Locks

🔰 Introduction to Thread Synchronization

Welcome to this comprehensive guide on Java thread synchronization! In the world of multi-threaded programming, one of the most critical challenges is ensuring that multiple threads can work together harmoniously without corrupting shared data or creating inconsistent states. This is where thread synchronization comes into play.

Thread synchronization is the mechanism that ensures that two or more concurrent threads don't simultaneously execute a critical section of a program, leading to unpredictable results. In Java, the primary means of achieving synchronization is through the synchronized keyword, which leverages intrinsic locks (also known as monitor locks) to control access to shared resources.

Whether you're building a responsive web application, a high-performance computing system, or a simple multi-threaded utility, understanding thread synchronization is essential for writing robust, reliable, and efficient concurrent code. In this tutorial, we'll dive deep into synchronized blocks and methods, intrinsic locks, and the differences between object-level and class-level synchronization.

🧠 Detailed Explanation of Thread Synchronization

What is Thread Synchronization?

Thread synchronization is the process of coordinating the execution of multiple threads to ensure they access shared resources in a controlled manner. Without proper synchronization, concurrent access to shared data can lead to:

  • Race conditions: When the behavior of a program depends on the relative timing of events, such as which thread executes first
  • Data corruption: When multiple threads modify the same data simultaneously, leading to inconsistent states
  • Visibility problems: When changes made by one thread are not visible to other threads

Java provides several mechanisms for thread synchronization, with the synchronized keyword being the most fundamental.

🔒 Synchronized Blocks and Methods

In Java, the synchronized keyword can be used in two ways:

  1. Synchronized Methods: Applying the synchronized keyword to a method
  2. Synchronized Blocks: Using the synchronized keyword with a specific object as a lock

Synchronized Methods

When you declare a method as synchronized, the entire method becomes a critical section. Only one thread can execute this method on the same object at a time.

public class Counter {
    private int count = 0;
    
    // Synchronized instance method
    public synchronized void increment() {
        count++;
    }
    
    // Synchronized static method
    public static synchronized void staticMethod() {
        // Critical section
    }
    
    public int getCount() {
        return count;
    }
}

In this example:

  • The increment() method is synchronized on the instance (object) level
  • The staticMethod() is synchronized on the class level
  • Only one thread can execute increment() on a specific Counter object at a time
  • Only one thread can execute staticMethod() at a time, regardless of how many Counter objects exist

Synchronized Blocks

Synchronized blocks provide more fine-grained control over synchronization by specifying exactly which object to use as the lock and which code section needs protection:

public class Counter {
    private int count = 0;
    private final Object lockObject = new Object();
    
    public void increment() {
        // Other non-synchronized code can go here
        
        synchronized(lockObject) {
            // Only this section is synchronized
            count++;
        }
        
        // More non-synchronized code can go here
    }
    
    public static void staticMethod() {
        synchronized(Counter.class) {
            // Synchronized on the Counter class
        }
    }
}

In this example:

  • Only the code within the synchronized(lockObject) block is protected
  • Other parts of the increment() method can be executed by multiple threads concurrently
  • The staticMethod() uses the Counter.class object as the lock

🔐 Intrinsic Locks (Monitor Locks)

Every object in Java has an associated intrinsic lock (also called a monitor lock). When a thread enters a synchronized block or method, it automatically acquires the intrinsic lock for the specified object. The lock is released when the thread exits the synchronized block or method.

How Intrinsic Locks Work

  1. When a thread attempts to enter a synchronized block/method, it tries to acquire the intrinsic lock of the specified object
  2. If the lock is available (not held by any other thread), the thread acquires it and enters the synchronized block
  3. If the lock is already held by another thread, the current thread is blocked (enters BLOCKED state) until the lock becomes available
  4. When the thread exits the synchronized block/method, it releases the lock, allowing other waiting threads to acquire it

Intrinsic Lock Characteristics

  • Reentrant: A thread can acquire the same lock multiple times. The lock keeps a count of how many times it has been acquired and must be released the same number of times before another thread can acquire it.
  • Mutual Exclusion: Only one thread can hold a particular lock at a time
  • Non-interruptible: A thread waiting to acquire a lock cannot be interrupted
  • Automatic Release: Locks are automatically released when a thread exits the synchronized block/method, even if it exits due to an exception

🔄 Object-level vs Class-level Locks

Java provides two levels of locking:

1. Object-level Locks (Instance Locks)

Object-level locks are associated with a specific instance of a class. They are used when:

  • You synchronize an instance method: public synchronized void method()
  • You synchronize on an object: synchronized(this) or synchronized(objectReference)
public class BankAccount {
    private double balance;
    
    // Object-level synchronization
    public synchronized void deposit(double amount) {
        balance += amount;
    }
    
    // Equivalent to the above
    public void withdraw(double amount) {
        synchronized(this) {
            balance -= amount;
        }
    }
}

With object-level locks:

  • Different threads can execute synchronized methods on different objects simultaneously
  • Only one thread can execute a synchronized method on the same object at a time

2. Class-level Locks (Static Locks)

Class-level locks are associated with the class itself, not with any specific instance. They are used when:

  • You synchronize a static method: public static synchronized void method()
  • You synchronize on a class literal: synchronized(ClassName.class)
public class Logger {
    private static final List<String> log = new ArrayList<>();
    
    // Class-level synchronization
    public static synchronized void addLog(String message) {
        log.add(message);
    }
    
    // Equivalent to the above
    public static void clearLog() {
        synchronized(Logger.class) {
            log.clear();
        }
    }
}

With class-level locks:

  • Only one thread can execute a static synchronized method in the class at a time
  • All instances of the class share the same class lock
  • Class-level locks don't affect object-level locks and vice versa

🔄 Visual Representation of Locks

Let's visualize how object-level and class-level locks work:

Object-level Locks:
┌─────────────────┐  ┌─────────────────┐  ┌─────────────────┐
│  Object A       │  │  Object B       │  │  Object C       │
│  ┌───────────┐  │  │  ┌───────────┐  │  │  ┌───────────┐  │
│  │ Lock for  │  │  │  │ Lock for  │  │  │  │ Lock for  │  │
│  │ Object A  │  │  │  │ Object B  │  │  │  │ Object C  │  │
│  └───────────┘  │  │  └───────────┘  │  │  └───────────┘  │
└─────────────────┘  └─────────────────┘  └─────────────────┘

Class-level Lock:
┌───────────────────────────────────────────────────────────┐
│  Class                                                     │
│  ┌───────────────────────────────────────────────────┐    │
│  │               Lock for the Class                   │    │
│  └───────────────────────────────────────────────────┘    │
└───────────────────────────────────────────────────────────┘

💻 Example with Code Comments

Let's look at a complete example that demonstrates synchronized blocks, methods, and both object-level and class-level locks:

public class BankAccount {
    private double balance;
    private final String accountNumber;
    private static int totalAccounts = 0;
    private static final Object classLock = new Object(); // Explicit lock for class-level operations
    
    public BankAccount(String accountNumber, double initialBalance) {
        this.accountNumber = accountNumber;
        this.balance = initialBalance;
        
        // Using class-level synchronization for a shared counter
        synchronized(BankAccount.class) {
            totalAccounts++; // Increment the static counter safely
        }
    }
    
    // Object-level synchronized method
    // Only one thread can access this method for a specific BankAccount instance
    public synchronized void deposit(double amount) {
        if (amount <= 0) {
            throw new IllegalArgumentException("Deposit amount must be positive");
        }
        
        // This entire method is protected by the intrinsic lock of this BankAccount instance
        double newBalance = balance + amount;
        
        // Simulating some processing time to make concurrency issues more likely
        try {
            Thread.sleep(50);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
        
        balance = newBalance;
        System.out.println("Deposited: " + amount + " to account " + accountNumber + 
                           ", New balance: " + balance);
    }
    
    // Using a synchronized block for more fine-grained control
    public void withdraw(double amount) {
        if (amount <= 0) {
            throw new IllegalArgumentException("Withdrawal amount must be positive");
        }
        
        // Only the critical section is synchronized
        // Code outside this block can be executed by multiple threads concurrently
        synchronized(this) { // 'this' refers to the current BankAccount instance
            if (balance < amount) {
                throw new IllegalStateException("Insufficient funds");
            }
            
            double newBalance = balance - amount;
            
            // Simulating some processing time
            try {
                Thread.sleep(50);
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
            
            balance = newBalance;
        }
        
        // This code is outside the synchronized block and can be executed concurrently
        System.out.println("Withdrawn: " + amount + " from account " + accountNumber + 
                           ", New balance: " + getBalance());
    }
    
    // This method is not synchronized because it only reads the balance
    // However, this might lead to stale data if called while another thread is modifying the balance
    public double getBalance() {
        return balance;
    }
    
    // Class-level synchronized method
    // Only one thread can execute this method at a time, regardless of which BankAccount instance it's using
    public static synchronized int getTotalAccounts() {
        return totalAccounts;
    }
    
    // Using an explicit lock object for class-level synchronization
    public static void printStatistics() {
        synchronized(classLock) {
            System.out.println("Total accounts: " + totalAccounts);
            // Other statistics...
        }
    }
    
    // Main method to demonstrate the BankAccount class
    public static void main(String[] args) {
        // Create a shared account
        BankAccount account = new BankAccount("12345", 1000);
        
        // Create multiple threads that deposit to the same account
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 5; i++) {
                account.deposit(100);
            }
        }, "DepositThread-1");
        
        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 5; i++) {
                account.deposit(200);
            }
        }, "DepositThread-2");
        
        Thread t3 = new Thread(() -> {
            for (int i = 0; i < 3; i++) {
                account.withdraw(300);
            }
        }, "WithdrawThread");
        
        // Start all threads
        t1.start();
        t2.start();
        t3.start();
        
        // Wait for all threads to complete
        try {
            t1.join();
            t2.join();
            t3.join();
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
        
        // Print final balance
        System.out.println("Final balance: " + account.getBalance());
        System.out.println("Total accounts: " + BankAccount.getTotalAccounts());
    }
}

This example demonstrates:

  1. Object-level synchronization with the deposit() method
  2. Fine-grained synchronization with a synchronized block in the withdraw() method
  3. Class-level synchronization with the static getTotalAccounts() method
  4. Using an explicit lock object for class-level synchronization in printStatistics()
  5. Multiple threads safely accessing the same account

📦 More Code Snippets

1. Using Different Lock Objects for Different Resources

public class ResourceManager {
    private final Object resourceALock = new Object();
    private final Object resourceBLock = new Object();
    
    private Resource resourceA;
    private Resource resourceB;
    
    public void operateOnResourceA() {
        synchronized(resourceALock) {
            // Operations on resourceA
            resourceA.use();
        }
    }
    
    public void operateOnResourceB() {
        synchronized(resourceBLock) {
            // Operations on resourceB
            resourceB.use();
        }
    }
    
    public void operateOnBothResources() {
        synchronized(resourceALock) {
            synchronized(resourceBLock) {
                // Operations on both resources
                resourceA.use();
                resourceB.use();
            }
        }
    }
}

2. Synchronized Collections vs. Explicit Synchronization

import java.util.*;
import java.util.concurrent.*;

public class CollectionSynchronizationExample {
    public static void main(String[] args) {
        // Using synchronized collections
        List<String> synchronizedList = Collections.synchronizedList(new ArrayList<>());
        
        // Using concurrent collections (generally preferred)
        List<String> concurrentList = new CopyOnWriteArrayList<>();
        Map<String, Integer> concurrentMap = new ConcurrentHashMap<>();
        
        // Using explicit synchronization with regular collections
        List<String> list = new ArrayList<>();
        
        // Adding elements safely
        synchronized(list) {
            list.add("item1");
            list.add("item2");
        }
        
        // Iterating safely
        synchronized(list) {
            for (String item : list) {
                System.out.println(item);
            }
        }
    }
}

3. Synchronized Methods vs. Synchronized Blocks

public class SynchronizationComparison {
    private int counter = 0;
    private final Object lock = new Object();
    
    // Approach 1: Synchronized method
    public synchronized void incrementMethod() {
        counter++;
        // Entire method is synchronized
    }
    
    // Approach 2: Synchronized block
    public void incrementBlock() {
        // Code before synchronized block runs without synchronization
        doSomethingBeforeSynchronization();
        
        synchronized(this) {
            counter++;
        }
        
        // Code after synchronized block runs without synchronization
        doSomethingAfterSynchronization();
    }
    
    // Approach 3: Using a dedicated lock object
    public void incrementWithDedicatedLock() {
        synchronized(lock) {
            counter++;
        }
    }
    
    private void doSomethingBeforeSynchronization() {
        // Non-critical operations
    }
    
    private void doSomethingAfterSynchronization() {
        // Non-critical operations
    }
}

🚀 Why It Matters / Use Cases

Understanding thread synchronization is crucial for several reasons:

1. Data Integrity

Without proper synchronization, concurrent access to shared data can lead to corruption and inconsistent states. Synchronization ensures that data modifications are atomic and visible to all threads.

Real-world example: Banking systems where multiple transactions might try to modify the same account balance simultaneously.

2. Performance Optimization

While synchronization is necessary for correctness, excessive synchronization can lead to performance bottlenecks. Understanding the different synchronization mechanisms allows you to choose the most appropriate one for your specific needs.

Real-world example: High-performance web servers that need to handle thousands of concurrent connections while maintaining data consistency.

3. Deadlock Prevention

Improper use of synchronization can lead to deadlocks, where threads are permanently blocked waiting for each other. Understanding synchronization helps you design your code to avoid such scenarios.

Real-world example: Resource allocation systems where multiple processes request access to shared resources.

4. Common Use Cases

Web Applications

  • Handling concurrent user sessions
  • Managing connection pools
  • Caching frequently accessed data

Database Systems

  • Transaction processing
  • Concurrent query execution
  • Connection management

Real-time Systems

  • Sensor data processing
  • Event handling
  • Control systems

Parallel Computing

  • Dividing work among multiple processors
  • Aggregating results from parallel computations
  • Coordinating worker threads

🧭 Best Practices / Rules to Follow

1. Minimize the Scope of Synchronization

✅ DO:

  • Synchronize only the critical sections of your code
  • Use synchronized blocks instead of synchronized methods when possible
  • Release locks as soon as you're done with the critical section

❌ DON'T:

  • Synchronize entire methods if only a small part needs protection
  • Hold locks longer than necessary
  • Perform lengthy operations while holding a lock
// GOOD: Minimized synchronization scope
public void processData(List<String> data) {
    // Pre-processing (not synchronized)
    List<String> processedData = preProcess(data);
    
    // Only synchronize the critical section
    synchronized(this) {
        for (String item : processedData) {
            sharedResource.add(item);
        }
    }
    
    // Post-processing (not synchronized)
    postProcess();
}

// BAD: Excessive synchronization
public synchronized void processDataBad(List<String> data) {
    // Everything is synchronized, even operations that don't need it
    List<String> processedData = preProcess(data);
    
    for (String item : processedData) {
        sharedResource.add(item);
    }
    
    postProcess();
}

2. Be Consistent with Lock Objects

✅ DO:

  • Use the same lock object for protecting related data
  • Document which lock protects which data
  • Consider using private final lock objects for explicit control

❌ DON'T:

  • Use different locks to protect the same data
  • Use mutable objects as locks
  • Use string literals or boxed primitives as locks (due to interning)
// GOOD: Consistent lock usage
public class UserManager {
    private final Map<String, User> users = new HashMap<>();
    private final Object usersLock = new Object(); // Dedicated lock
    
    public void addUser(User user) {
        synchronized(usersLock) {
            users.put(user.getId(), user);
        }
    }
    
    public User getUser(String id) {
        synchronized(usersLock) {
            return users.get(id);
        }
    }
}

// BAD: Inconsistent lock usage
public class UserManagerBad {
    private final Map<String, User> users = new HashMap<>();
    
    public void addUser(User user) {
        synchronized(this) { // Using 'this' as lock
            users.put(user.getId(), user);
        }
    }
    
    public User getUser(String id) {
        synchronized(users) { // Using 'users' as lock - inconsistent!
            return users.get(id);
        }
    }
}

3. Avoid Nested Locks

✅ DO:

  • Acquire locks in a consistent order to prevent deadlocks
  • Release locks in the reverse order of acquisition
  • Consider using higher-level concurrency utilities for complex scenarios

❌ DON'T:

  • Acquire locks in different orders in different parts of your code
  • Call unknown methods while holding a lock (they might acquire other locks)
  • Create complex nested locking structures
// GOOD: Consistent lock ordering
public void transferMoney(Account from, Account to, double amount) {
    // Always lock accounts in a consistent order to prevent deadlocks
    Account firstLock = from.getId() < to.getId() ? from : to;
    Account secondLock = from.getId() < to.getId() ? to : from;
    
    synchronized(firstLock) {
        synchronized(secondLock) {
            if (from.getBalance() < amount) {
                throw new InsufficientFundsException();
            }
            from.debit(amount);
            to.credit(amount);
        }
    }
}

// BAD: Inconsistent lock ordering can lead to deadlocks
public void transferMoneyBad(Account from, Account to, double amount) {
    synchronized(from) {
        synchronized(to) {
            // If another thread calls transferMoney(to, from, amount),
            // it will lock 'to' first, then try to lock 'from'
            // This can lead to a deadlock
            from.debit(amount);
            to.credit(amount);
        }
    }
}

4. Consider Alternatives to Intrinsic Locks

✅ DO:

  • Use java.util.concurrent.locks for more advanced locking needs
  • Consider using atomic variables for simple counters and flags
  • Use concurrent collections when appropriate

❌ DON'T:

  • Reinvent the wheel by creating your own locking mechanisms
  • Use synchronized blocks when a simpler solution exists
  • Ignore the rich concurrency utilities provided by Java
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.atomic.AtomicInteger;

public class ModernConcurrencyExample {
    // Using explicit locks
    private final ReentrantLock lock = new ReentrantLock();
    
    // Using atomic variables
    private final AtomicInteger counter = new AtomicInteger(0);
    
    public void incrementWithExplicitLock() {
        lock.lock();
        try {
            // Critical section
            // More flexible than synchronized blocks
        } finally {
            lock.unlock(); // Always release the lock in a finally block
        }
    }
    
    public void incrementCounter() {
        // Atomic operation, no explicit locking needed
        counter.incrementAndGet();
    }
}

5. Be Aware of Synchronization Overhead

✅ DO:

  • Measure the performance impact of synchronization
  • Use synchronization judiciously
  • Consider whether synchronization is actually needed

❌ DON'T:

  • Synchronize everything "just to be safe"
  • Ignore the performance implications of synchronization
  • Use thread-local variables when shared state isn't needed
// GOOD: Using ThreadLocal for thread-confined data
public class UserContext {
    private static final ThreadLocal<User> currentUser = new ThreadLocal<>();
    
    public static void setCurrentUser(User user) {
        currentUser.set(user);
    }
    
    public static User getCurrentUser() {
        return currentUser.get();
    }
    
    public static void clear() {
        currentUser.remove();
    }
}

⚠️ Common Pitfalls or Gotchas

1. Synchronization Doesn't Guarantee Ordering

Just because code is synchronized doesn't mean it will execute in a specific order. The JVM and OS scheduler determine which thread runs when.

// This doesn't guarantee that thread1 will run before thread2
Thread thread1 = new Thread(() -> {
    synchronized(lock) {
        // Critical section
    }
});

Thread thread2 = new Thread(() -> {
    synchronized(lock) {
        // Critical section
    }
});

thread1.start();
thread2.start();

2. The "Check-Then-Act" Race Condition

One of the most common concurrency bugs occurs when you check a condition and then act on it without proper synchronization.

// INCORRECT: Race condition
if (!map.containsKey("key")) {  // Check
    map.put("key", "value");    // Act
}

// CORRECT: Synchronized check-then-act
synchronized(map) {
    if (!map.containsKey("key")) {
        map.put("key", "value");
    }
}

// ALTERNATIVE: Use ConcurrentHashMap
ConcurrentHashMap<String, String> concurrentMap = new ConcurrentHashMap<>();
concurrentMap.putIfAbsent("key", "value");

3. Deadlocks

Deadlocks occur when two or more threads are blocked forever, each waiting for the other to release a lock.

// Potential deadlock scenario
Thread thread1 = new Thread(() -> {
    synchronized(lockA) {
        // Do something
        synchronized(lockB) {
            // Do something else
        }
    }
});

Thread thread2 = new Thread(() -> {
    synchronized(lockB) {
        // Do something
        synchronized(lockA) {
            // Do something else
        }
    }
});

thread1.start();
thread2.start();

To avoid deadlocks:

  • Acquire locks in a consistent order
  • Use timeout versions of lock acquisition when possible
  • Avoid holding locks while calling external methods

4. Livelock

Livelocks occur when threads keep changing their state in response to other threads, preventing any of them from making progress.

// Potential livelock scenario
while (!lockAcquired) {
    if (tryLock()) {
        lockAcquired = true;
    } else {
        // Release any resources and try again
        // If all threads do this, they might keep retrying without progress
        Thread.yield();
    }
}

5. Using String Literals as Locks

String literals are interned in Java, which means that different parts of your code might inadvertently use the same lock.

// DANGEROUS: Using string literals as locks
synchronized("lock") {
    // Critical section
}

// BETTER: Use dedicated final lock objects
private static final Object LOCK = new Object();

synchronized(LOCK) {
    // Critical section
}

6. Forgetting That wait() Releases the Lock

When a thread calls wait(), it releases the lock and waits to be notified. This can lead to confusion if you expect the lock to be held.

synchronized(lock) {
    while (!condition) {
        lock.wait(); // Releases the lock while waiting
    }
    // When notified and condition is true, the thread reacquires the lock and continues
}

7. Synchronization and Inheritance

When overriding synchronized methods, the synchronized keyword is not inherited. You must explicitly declare the overriding method as synchronized if needed.

class Parent {
    public synchronized void method() {
        // Synchronized implementation
    }
}

class Child extends Parent {
    @Override
    public void method() {
        // NOT synchronized unless explicitly declared so
        super.method(); // This call is synchronized
    }
    
    @Override
    public synchronized void anotherMethod() {
        // Properly synchronized override
        super.anotherMethod();
    }
}

📌 Summary / Key Takeaways

  • Thread Synchronization is essential for ensuring data integrity in multi-threaded applications.

  • Synchronized Methods:

    • Entire method is synchronized
    • Uses the object instance (this) as the lock for instance methods
    • Uses the class object as the lock for static methods

  • Synchronized Blocks:

    • More fine-grained control over synchronization
    • Can specify which object to use as the lock
    • Only the code within the block is synchronized

  • Intrinsic Locks (Monitor Locks):

    • Every object in Java has an associated intrinsic lock
    • Locks are reentrant (the same thread can acquire the same lock multiple times)
    • Locks are automatically released when the thread exits the synchronized block/method

  • Object-level vs Class-level Locks:

    • Object-level locks protect instance data and are specific to each object instance
    • Class-level locks protect static data and are shared across all instances of the class
    • Both types of locks can be used independently

  • Best Practices:

    • Minimize the scope of synchronization
    • Be consistent with lock objects
    • Avoid nested locks or acquire them in a consistent order
    • Consider alternatives like java.util.concurrent.locks and atomic variables
    • Be aware of synchronization overhead

  • Common Pitfalls:

    • Race conditions in check-then-act scenarios
    • Deadlocks from inconsistent lock ordering
    • Using string literals or boxed primitives as locks
    • Forgetting that wait() releases the lock
    • Not accounting for inheritance with synchronized methods

🧩 Exercises or Mini-Projects

Exercise 1: Bank Account Synchronization

Create a multi-threaded banking application that simulates concurrent deposits and withdrawals from multiple accounts. Implement proper synchronization to ensure that account balances remain consistent.

Requirements:

  • Create a BankAccount class with methods for deposit and withdrawal
  • Implement a Bank class that manages multiple accounts
  • Create a TransferManager that can transfer money between accounts
  • Implement a method to detect and prevent deadlocks during transfers
  • Create multiple threads that perform random operations on random accounts
  • Verify that the final account balances are consistent

Exercise 2: Thread-Safe Singleton Implementation

Implement a thread-safe singleton class using different synchronization techniques and compare their performance.

Requirements:

  • Implement the singleton using the following approaches:
    • Eager initialization
    • Lazy initialization with synchronized method
    • Double-checked locking
    • Initialization-on-demand holder idiom
  • Create a multi-threaded test harness to verify thread safety
  • Measure and compare the performance of each implementation
  • Identify potential issues with each approach

By mastering thread synchronization in Java, you'll be well-equipped to build robust, efficient concurrent applications. Remember that synchronization is a powerful tool, but it must be used judiciously to avoid performance bottlenecks and concurrency issues. Practice these concepts, experiment with different approaches, and always test your multi-threaded code thoroughly.

Happy coding!

Executors & ExecutorService
Volatile and Atomicity