From 86882ca1971706defd27c06f25dc77de911d5fa0 Mon Sep 17 00:00:00 2001
From: Mobina <mbnqnra@gmail.com>
Date: Fri, 17 Jul 2026 23:02:03 +0330
Subject: [PATCH] Completion of the specified parts

---
 Answers.md                                    | 43 ++++++++++++++
 .../java/dev/banking/model/BankAccount.java   | 57 +++++++++++++++++--
 2 files changed, 96 insertions(+), 4 deletions(-)
 create mode 100644 Answers.md

diff --git a/Answers.md b/Answers.md
new file mode 100644
index 0000000..dde4642
--- /dev/null
+++ b/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());
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/dev/banking/model/BankAccount.java b/src/main/java/dev/banking/model/BankAccount.java
index 745ede2..a2782ac 100644
--- a/src/main/java/dev/banking/model/BankAccount.java
+++ b/src/main/java/dev/banking/model/BankAccount.java
@@ -4,6 +4,7 @@ public class BankAccount {
 
     private final int accountId;
     private long balance;
+    private final ReentrantLock lock = new ReentrantLock();
 
     /*
      * Students may introduce additional fields
@@ -32,7 +33,16 @@ 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 +53,14 @@ 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 +73,12 @@ 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 +95,33 @@ 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();
+        }
+
     }
 }
\ No newline at end of file