Java Programmer Skills Programme

📘LESSON 4

3.1 Lesson Outcomes

After completing this lesson, learners will be able to:

Explain synchronized operations in Java.
Identify problems associated with synchronized methods.
Explain atomic classes in Java.
Explain the need for Concurrent Maps.
Describe how ConcurrentHashMap uses different locks.
Explain Copy-On-Write concurrent collections.

3.2 Overview

Modern Java applications often process multiple tasks simultaneously using multithreading and concurrent programming. When multiple threads access shared data, concurrency problems may occur. Java provides synchronization mechanisms, atomic classes, and concurrent collections to improve thread safety and application performance.

This lesson introduces learners to concurrency concepts and explains synchronized operations, atomic operations, concurrent maps, and concurrent collections used in Java applications.

Concurrency is widely used in:

banking systems,
enterprise applications,
cloud platforms,
web applications,
and distributed systems.

Understanding concurrency is important because modern software systems rely heavily on multithreaded processing and thread-safe operations.

KT0401 — Synchronized

The:

synchronized

keyword controls access to shared resources in multithreaded environments.

Synchronization allows only one thread to access a synchronized block or method at a time.

Synchronized Method Example

public synchronized void increment() {

    counter++;
}

Importance of Synchronization

Synchronization helps:

prevent data corruption,
avoid race conditions,
and improve thread safety.

KT0402 — Problem with Synchronized

Although synchronization improves thread safety, it may create performance problems.

Problems with Synchronized

Problem	Description
Slower Performance	Threads wait for locks
Blocking	Threads become delayed
Reduced Scalability	Limits concurrent execution

Example Problem

When many threads wait for the same synchronized method:

execution becomes slower,
and application performance decreases.

Importance of Understanding Synchronization Problems

Understanding synchronization limitations helps developers:

improve performance,
optimize concurrency,
and design efficient systems.

KT0403 — Atomic Classes

Atomic classes perform thread-safe operations without full synchronization.

Atomic classes belong to:

java.util.concurrent.atomic

package.

Example Atomic Class

AtomicInteger counter =
        new AtomicInteger(0);

Increment Example

counter.incrementAndGet();

Benefits of Atomic Classes

Atomic classes provide:

faster performance,
thread safety,
and lock-free operations.

Importance of Atomic Classes

Atomic classes improve:

concurrency performance,
efficiency,
and thread-safe processing.

KT0404 — Need for Concurrent Map

Regular HashMap is not thread-safe in multithreaded environments.

Concurrent Maps are required when:

multiple threads access shared data simultaneously.

Problems with Normal HashMap

Problem	Description
Data Corruption	Simultaneous updates
Inconsistent Results	Unsafe concurrent access
Race Conditions	Multiple thread conflicts

Importance of Concurrent Maps

Concurrent Maps improve:

thread safety,
scalability,
and concurrent processing.

KT0405 — Concurrent HashMap Uses Different Locks for Different Regions

ConcurrentHashMap improves concurrency by using separate locks for different regions of the map.

This allows:

multiple threads to work simultaneously,
without locking the entire structure.

Example

ConcurrentHashMap<Integer, String> map =
        new ConcurrentHashMap<Integer, String>();

Advantages of ConcurrentHashMap

Advantage	Description
Better Performance	Reduced blocking
Thread Safety	Safe concurrent access
Scalability	Supports many threads

Importance of ConcurrentHashMap

ConcurrentHashMap improves:

concurrent data processing,
performance,
and scalability.

KT0406 — Copy On Write Concurrent Collections

Copy-On-Write collections create a new copy of the collection whenever modifications occur.

These collections are useful when:

reads are more common than writes.

Example

CopyOnWriteArrayList<String> names =
        new CopyOnWriteArrayList<String>();

Characteristics of Copy-On-Write Collections

Characteristic	Description
Safe Iteration	No concurrent modification errors
Thread Safe	Supports concurrent access
Higher Memory Usage	Creates copies during updates

Importance of Copy-On-Write Collections

Copy-On-Write collections improve:

thread safety,
concurrent reading,
and stable iteration.

3.5 Key Notes / Summary

synchronized controls access to shared resources.
Synchronization may reduce performance.
Atomic classes provide lock-free thread safety.
Concurrent Maps support safe multithreaded access.
ConcurrentHashMap uses multiple locks for better performance.
Copy-On-Write collections improve safe concurrent iteration.
Concurrency improves multithreaded application processing.