feat: add advanced multithreading banking system skeleton

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

@@ -0,0 +1,48 @@
+package dev.banking.model;
+
+public class BankAccount {
+
+    private final int accountId;
+    private long balance;
+
+    public BankAccount(int accountId, long initialBalance) {
+        this.accountId = accountId;
+        this.balance = initialBalance;
+    }
+
+    public int getAccountId() {
+        return accountId;
+    }
+
+    /*
+     * TODO
+     * Implement a thread-safe balance reader.
+     */
+    public long getBalance() {
+        throw new UnsupportedOperationException();
+    }
+
+    /*
+     * TODO
+     * Implement a thread-safe deposit operation.
+     */
+    public void deposit(int amount) {
+        throw new UnsupportedOperationException();
+    }
+
+    /*
+     * TODO
+     * Implement a thread-safe withdrawal operation.
+     */
+    public void withdraw(int amount) {
+        throw new UnsupportedOperationException();
+    }
+
+    /*
+     * TODO
+     * Implement an atomic and deadlock-free transfer.
+     */
+    public void transfer(BankAccount target, int amount) {
+        throw new UnsupportedOperationException();
+    }
+}

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

@@ -0,0 +1,39 @@
+package dev.banking.model;
+
+public class Transaction {
+
+    private final TransactionType type;
+
+    private final int sourceAccountId;
+    private final int targetAccountId;
+
+    private final int amount;
+
+    public Transaction(
+            TransactionType type,
+            int sourceAccountId,
+            int targetAccountId,
+            int amount
+    ) {
+        this.type = type;
+        this.sourceAccountId = sourceAccountId;
+        this.targetAccountId = targetAccountId;
+        this.amount = amount;
+    }
+
+    public TransactionType getType() {
+        return type;
+    }
+
+    public int getSourceAccountId() {
+        return sourceAccountId;
+    }
+
+    public int getTargetAccountId() {
+        return targetAccountId;
+    }
+
+    public int getAmount() {
+        return amount;
+    }
+}

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

@@ -0,0 +1,7 @@
+package dev.banking.model;
+
+public enum TransactionType {
+    DEPOSIT,
+    WITHDRAW,
+    TRANSFER
+}