adding bonus part

.idea/compiler.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="CompilerConfiguration">
+    <annotationProcessing>
+      <profile name="Maven default annotation processors profile" enabled="true">
+        <sourceOutputDir name="target/generated-sources/annotations" />
+        <sourceTestOutputDir name="target/generated-test-sources/test-annotations" />
+        <outputRelativeToContentRoot value="true" />
+        <module name="HW-09-Advanced-Multithreading" />
+      </profile>
+    </annotationProcessing>
+  </component>
+</project>

.idea/encodings.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Encoding">
+    <file url="file://$PROJECT_DIR$/src/main/java" charset="UTF-8" />
+    <file url="file://$PROJECT_DIR$/src/main/resources" charset="UTF-8" />
+  </component>
+</project>

.idea/jarRepositories.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="RemoteRepositoriesConfiguration">
+    <remote-repository>
+      <option name="id" value="central" />
+      <option name="name" value="Maven Central repository" />
+      <option name="url" value="https://repo1.maven.org/maven2" />
+    </remote-repository>
+    <remote-repository>
+      <option name="id" value="jboss.community" />
+      <option name="name" value="JBoss Community repository" />
+      <option name="url" value="https://repository.jboss.org/nexus/content/repositories/public/" />
+    </remote-repository>
+    <remote-repository>
+      <option name="id" value="central" />
+      <option name="name" value="Central Repository" />
+      <option name="url" value="https://mirror-maven.runflare.com/maven2" />
+    </remote-repository>
+  </component>
+</project>

.idea/misc.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="MavenProjectsManager">
+    <option name="originalFiles">
+      <list>
+        <option value="$PROJECT_DIR$/pom.xml" />
+      </list>
+    </option>
+  </component>
+  <component name="ProjectRootManager" version="2" project-jdk-name="25" project-jdk-type="JavaSDK" />
+</project>

.idea/vcs.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+  </component>
+</project>

Answers.md

@@ -0,0 +1,43 @@
+1 -
+زمانی که میخواهیم عملیات های ساده روی یک متغیر داخل thread انجام دهیم یک شیئ atomic variable داخل آن نخ میسازیم و برای انجام عملیات از توابع داخل آن کلاس استفاده میکنیم.
+این متغیر ها این خصوصیت را دارند که هنگامی که عملیاتی روی آن درحال اجراست thread دیگری اجرا نمیشود در نتیجه در محاسبه مقدار خطا ایجاد نمیشود.
+
+2 -
+AtomicInteger, AtomicLong, AtomicBoolean, AtomicReference<T>
+
+3 - Compare locks with atomic variables.
+متغیر های اتمی برای عملیات های ساده استفاده میشود اما قفل برای عملیات های پیچیده تر استفاده میشود و برای چند متغیر استفاده میشود.
+
+🎯Bonus Task:
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class AtomicDemo {
+
+    private static int normalCounter = 0;
+    private static AtomicInteger atomicCounter = new AtomicInteger(0);
+
+    public static void main(String[] args) throws InterruptedException {
+
+        Thread[] threads = new Thread[10];
+
+        for (int i = 0; i < threads.length; i++) {
+            threads[i] = new Thread(() -> {
+                for (int j = 0; j < 10000; j++) {
+                    normalCounter++;
+                    atomicCounter.incrementAndGet();
+                }
+            });
+        }
+
+        for (Thread t : threads) {
+            t.start();
+        }
+
+        for (Thread t : threads) {
+            t.join();
+        }
+
+        System.out.println( normalCounter);
+        System.out.println( atomicCounter.get());
+    }
+}

src/main/java/dev/banking/model/BankAccount.java

@@ -1,9 +1,12 @@
 package dev.banking.model;
 
+import java.util.concurrent.locks.ReentrantLock;
+
 public class BankAccount {
 
     private final int accountId;
     private long balance;
+    private final ReentrantLock lock = new ReentrantLock();
 
     /*
      * Students may introduce additional fields
@@ -32,7 +35,16 @@ public class BankAccount {
      * - Should not block unnecessarily if using read/write locks
      */
     public long getBalance() {
-        throw new UnsupportedOperationException("TODO: implement thread-safe balance read");
+
+
+                lock.lock();
+                try{
+                    return balance;
+                }finally {
+                    lock.unlock();
+                }
+
+
     }
 
     /*
@@ -43,7 +55,14 @@ public class BankAccount {
      * - Must not lose updates under concurrency
      */
     public void deposit(long amount) {
-        throw new UnsupportedOperationException("TODO: implement thread-safe deposit");
+
+        lock.lock();
+        try{
+            balance+=amount;
+        }finally {
+            lock.unlock();
+        }
+
     }
 
     /*
@@ -56,7 +75,12 @@ public class BankAccount {
      *   to extend the system (optional)
      */
     public void withdraw(long amount) {
-        throw new UnsupportedOperationException("TODO: implement thread-safe withdraw");
+        lock.lock();
+        try{
+            balance-=amount;
+        }finally {
+            lock.unlock();
+        }
     }
 
     /*
@@ -73,6 +97,33 @@ public class BankAccount {
      * - Or tryLock with retry strategy
      */
     public void transfer(BankAccount target, long amount) {
-        throw new UnsupportedOperationException("TODO: implement atomic deadlock-free transfer");
+        BankAccount first;
+        BankAccount second;
+
+        if (this == target) {
+            return;
+        }
+
+        if (this.getAccountId() < target.getAccountId()) {
+            first = this;
+            second = target;
+        } else {
+            first = target;
+            second = this;
+        }
+
+        first.lock.lock();
+        try {
+            second.lock.lock();
+            try {
+                this.balance -= amount;
+                target.balance += amount;
+            } finally {
+                second.lock.unlock();
+            }
+        } finally {
+            first.lock.unlock();
+        }
+
     }
 }