From 2efd5e3e350bd98b7e464b2247b2f0f18897f705 Mon Sep 17 00:00:00 2001
From: Farnam Jahangard <farnamjahangard@gmail.com>
Date: Wed, 10 Jun 2026 17:33:46 +0330
Subject: [PATCH] answered theoretical questions finished the bonus task in
 theoretical questions part

---
 ANSWERS.md                              | 54 +++++++++++++++++++++++++
 src/main/java/bonus/AtomicVsNormal.java | 42 +++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 ANSWERS.md
 create mode 100644 src/main/java/bonus/AtomicVsNormal.java

diff --git a/ANSWERS.md b/ANSWERS.md
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+# Answers
+
+## Q1
+Atomic variable is a type of variable that combines all three process of: read, write and update into a single operation.  
+as an example when we write `i++` it may seem like a single operation  
+but the compiler needs to read `i`(read), add 1 to it (update) and change `i` to new value (write)  
+since all these operations are combined into one operation race conditions doesn't occur  
+unlike normal variables.
+
+## Q2
+`AtomicInteeger`, `AtomicBoolean`.`AtomicLong` & `AtomicReference`
+
+#### `AtomicInteeger` Use case
+used as counters that are shared across threads
+#### `AtomicBoolean` Use case
+used as flags that are used across threads (like `running` flag)
+#### `AtomicLong` Use case
+in general anything that needs long operations for multiple threads such as a bank account balance or an id counter
+#### `AtomicReference` Use case
+it's used whenever you need atomic operations on any object 
+
+## Q3
+locks are used to lock a full block of code, this prevents race conditions as a thread locks the section it's working on when it reaches it
+
+therefore we should use locks when we wan't to prevent race conditions for a block of code  
+and use atomic variables on more basic things
+## Q4
+this situation may occur because if there are too many threads trying to access a shared resource performance drops because workers sleep more than they do work
+
+#### Usage of locks
+locks make a block of code completely unaccessible for every thread except one
+this would cause those other threads to sleep meaning even if you have 100 threads only one of them can work at a time.
+
+#### Usage of atomic variables
+when we use atomic variables and atomic operations, at a curtain point many threads my try to change one variable   
+only one can successfully access the variable, meaning the rest would fail  
+this failure is just waste of cpu power.
+
+## Q5
+majority of mainstream cpus has something around 8 to 16 cores right now  
+this means one thing  
+logically we can't run 100 threads at the same time in parallel  
+this causes something known as context switching: cpu cores need to switch between threads 
+and this continuous switching would make the program slow
+
+
+cpu cores have their own distinct cache, when a core changes a synced variable all the cpu cores change their cache value of that variable
+when we have too many threads working on a synced variable, cpu cores constantly follow the changes in order to keep their cache synced 
+this would cause cpu cores to spend more time synchronizing the cache rather than processing the threads 
+this situation is known cache coherence synchronization overhead.
+
+## Q6
+Deadlocks are rare because you can't determine threads execution order, OS determines this by itself
+to increase likelihood of deadlocks to happen a developer can start too many threads and delay the threads
\ No newline at end of file
diff --git a/src/main/java/bonus/AtomicVsNormal.java b/src/main/java/bonus/AtomicVsNormal.java
new file mode 100644
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+++ b/src/main/java/bonus/AtomicVsNormal.java
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+package bonus;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class AtomicVsNormal {
+    private static int counter = 0;
+    private static AtomicInteger atomicCounter = new AtomicInteger(0);
+
+    public static void main(String[] args){
+        int incrementCount = 1000;
+        List<Thread> workers = new ArrayList<>();
+
+        for (int i = 0; i < 10; i++){
+            workers.add(new Thread(() ->{
+                for (int j = 0; j < incrementCount; j++) {
+                    counter++;
+                    atomicCounter.incrementAndGet();
+                }
+            }
+        ));
+        }
+
+        for (Thread worker : workers){
+            worker.start();
+        }
+
+        for (Thread worker : workers){
+            try {
+                worker.join();
+            } catch (InterruptedException e) {
+                throw new RuntimeException(e);
+            }
+        }
+
+        System.out.println("Expected: 10000");
+        System.out.println("Normal increment: " + counter);
+        System.out.println("Atomic increment: " + atomicCounter.get());
+
+    }
+}