From 0128c5b759e53eb6c904e7db00b1e456938bd711 Mon Sep 17 00:00:00 2001 From: ShayanEdalatjoo Date: Fri, 10 Jul 2026 23:08:13 +0330 Subject: [PATCH] implementing BankAccount.java --- .idea/.gitignore | 10 ++ .idea/compiler.xml | 13 +++ .idea/encodings.xml | 7 ++ .idea/jarRepositories.xml | 20 ++++ .idea/misc.xml | 12 +++ .idea/vcs.xml | 6 ++ .../java/dev/banking/model/BankAccount.java | 92 ++++++++----------- 7 files changed, 104 insertions(+), 56 deletions(-) create mode 100644 .idea/.gitignore create mode 100644 .idea/compiler.xml create mode 100644 .idea/encodings.xml create mode 100644 .idea/jarRepositories.xml create mode 100644 .idea/misc.xml create mode 100644 .idea/vcs.xml diff --git a/.idea/.gitignore b/.idea/.gitignore new file mode 100644 index 0000000..ab1f416 --- /dev/null +++ b/.idea/.gitignore @@ -0,0 +1,10 @@ +# Default ignored files +/shelf/ +/workspace.xml +# Ignored default folder with query files +/queries/ +# Datasource local storage ignored files +/dataSources/ +/dataSources.local.xml +# Editor-based HTTP Client requests +/httpRequests/ diff --git a/.idea/compiler.xml b/.idea/compiler.xml new file mode 100644 index 0000000..812c3f9 --- /dev/null +++ b/.idea/compiler.xml @@ -0,0 +1,13 @@ + + + + + + + + + + + + + \ No newline at end of file diff --git a/.idea/encodings.xml b/.idea/encodings.xml new file mode 100644 index 0000000..aa00ffa --- /dev/null +++ b/.idea/encodings.xml @@ -0,0 +1,7 @@ + + + + + + + \ No newline at end of file diff --git a/.idea/jarRepositories.xml b/.idea/jarRepositories.xml new file mode 100644 index 0000000..a9076af --- /dev/null +++ b/.idea/jarRepositories.xml @@ -0,0 +1,20 @@ + + + + + + + + + + + \ No newline at end of file diff --git a/.idea/misc.xml b/.idea/misc.xml new file mode 100644 index 0000000..eba6e1f --- /dev/null +++ b/.idea/misc.xml @@ -0,0 +1,12 @@ + + + + + + + + \ No newline at end of file diff --git a/.idea/vcs.xml b/.idea/vcs.xml new file mode 100644 index 0000000..35eb1dd --- /dev/null +++ b/.idea/vcs.xml @@ -0,0 +1,6 @@ + + + + + + \ 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..f54d955 100644 --- a/src/main/java/dev/banking/model/BankAccount.java +++ b/src/main/java/dev/banking/model/BankAccount.java @@ -1,78 +1,58 @@ package dev.banking.model; +import java.util.concurrent.locks.Lock; +import java.util.concurrent.locks.ReentrantLock; + public class BankAccount { private final int accountId; private long balance; - - /* - * Students may introduce additional fields - * such as: - * - Lock / ReentrantLock - * - ReadWriteLock - * - Object monitor - * - etc. - */ - + private final Lock lock = new ReentrantLock(); public BankAccount(int accountId, long initialBalance) { this.accountId = accountId; this.balance = initialBalance; } - public int getAccountId() { return accountId; } - - /* - * TODO: - * Return the current balance in a thread-safe way. - * - * Requirements: - * - Must be safe under concurrent reads/writes - * - 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(); + } } - - /* - * TODO: - * Increase balance atomically. - * - * Requirements: - * - 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(); + } } - - /* - * TODO: - * Decrease balance atomically. - * - * Requirements: - * - Must not cause race conditions - * - Negative balance handling is NOT required unless you decide - * 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(); + } } - - /* - * TODO: - * Transfer money between two accounts atomically. - * - * IMPORTANT REQUIREMENTS: - * - Must be atomic (no partial transfer) - * - Must be deadlock-free - * - Must protect both source and target accounts - * - * HINT: - * - Consider global lock ordering using accountId - * - Or tryLock with retry strategy - */ public void transfer(BankAccount target, long amount) { - throw new UnsupportedOperationException("TODO: implement atomic deadlock-free transfer"); + BankAccount first = this.accountId < target.accountId ? this : target; + BankAccount second = this.accountId < target.accountId ? target : this; + first.lock.lock(); + try { + second.lock.lock(); + try { + this.withdraw(amount); + target.deposit(amount); + } finally { + second.lock.unlock(); + } + } finally { + first.lock.unlock(); + } } } \ No newline at end of file