Completion of the specified parts

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();
+        }
+
     }
 }