the previous runner class has been removed as its functionalities are…

… now embedded within the DigitalWallet class. A new class, WalletAccount encapsulates details and operations specific to a single user's wallet. Extensive methods have been added to DigitalWallet to support functionalities like account creation, balance transfer, and retrieving account statements.

src/main/java/live/ashish/cpjava/systemdesign/wallet/DigitalWallet.java

@@ -1,7 +1,115 @@
 package live.ashish.cpjava.systemdesign.wallet;
 
-//https://techwithkp.com/digital-wallet-design-machine-coding-round-solution/
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Scanner;
+
+/*
+https://onedrive.live.com/view.aspx?resid=9B1BD26B02F2442D%21153&id=documents&wd=target%285.%20Other%20Interview%20Questions%2FMachine%20Coding.one%7CFB04D0B9-D9F3-C944-B13B-DADD6AFC1934%2FDigital%20wallet%7CAB689DAE-4BBB-DB43-99BC-D0206D9082F3%2F%29
+onenote:https://d.docs.live.net/9b1bd26b02f2442d/Documents/notes/CP%20and%20Interview%20Notes/5.%20Other%20Interview%20Questions/Machine%20Coding.one#Digital%20wallet&section-id={FB04D0B9-D9F3-C944-B13B-DADD6AFC1934}&page-id={AB689DAE-4BBB-DB43-99BC-D0206D9082F3}&end
+ */
+
+// this is suboptimal, see the better version in link in the docs above
 public class DigitalWallet {
+    List<WalletAccount> walletAccountList = new ArrayList<>();
+    public static void main(String[] args) {
+        DigitalWallet wallet = new DigitalWallet();
+        Scanner input = new Scanner(System.in);
+        while (true) {
+            System.out.println("Please choose an option: \n1 - Create wallet" +
+                    "\n2 - Transfer Amount\n3 - Account Statement\n4 - Overview\n5 - Exit");
+            int response = input.nextInt();
+            input.nextLine();
+            switch (response) {
+                case 1:
+                    System.out.println("You have chosen: Create Wallet\nEnter name of user");
+                    String userName = input.nextLine();
+                    System.out.println("Enter amount in the wallet");
+                    double amount = input.nextDouble();
+                    wallet.createWalletAccount(userName,amount);
+                    break;
+                case 2:
+                    System.out.println("You have chosen: Transfer Amount\nEnter userId of payer");
+                    String sender = input.next();
+                    System.out.println("Enter userId of receiver");
+                    String receiver = input.next();
+                    System.out.println("Enter Amount to be sent..");
+                    double amountTransfer = input.nextDouble();
+                    wallet.transferAmount(sender,receiver,amountTransfer);
+                    break;
+                case 3:
+                    System.out.println("You have chosen: Account Statement\nEnter userId");
+                    String userId = input.next();
+                    wallet.accountStatement(userId);
+                    break;
+                case 4:
+                    System.out.println("You have chosen: Overview");
+                    // show all balances
+                    wallet.overview();
+                    break;
+                case 5:
+                    System.out.println("You have chosen: Exit");
+                    System.exit(0);
+                    break;
+                default:
+                    System.out.println("Invalid option, try again!!!");
+                    break;
+            }
+
+        }
+    }
+
+    private void overview() {
+        walletAccountList.forEach(System.out::println);
+    }
+
+    private void transferAmount(String sender, String receiver, double amountTransfer) {
+        WalletAccount senderAccount = null;
+        WalletAccount receiverAccount = null;
+        for (WalletAccount account : walletAccountList) {
+            if (account.getUserId().equals(sender)) {
+                senderAccount = account;
+            }
+            if (account.getUserId().equals(receiver)) {
+                receiverAccount = account;
+            }
+        }
+        if (senderAccount != null && receiverAccount != null) {
+            if (senderAccount.getAmountBalance() >= amountTransfer) {
+                senderAccount.setAmountBalance(senderAccount.getAmountBalance() - amountTransfer);
+                receiverAccount.setAmountBalance(receiverAccount.getAmountBalance() + amountTransfer);
+                senderAccount.getAccountStatement().add("sending amount: "+ amountTransfer +" to "+receiverAccount.getUserId());
+                receiverAccount.getAccountStatement().add("received amount: "+ amountTransfer +" from "+senderAccount.getUserId());
+                System.out.println("Amount transferred successfully!");
+                System.out.println("Balances, sender: "+ senderAccount.getAmountBalance()+ " receiver: "+receiverAccount.getAmountBalance());
+            } else {
+                System.out.println("Insufficient balance in sender's account!");
+            }
+        } else {
+            System.out.println("Invalid sender or receiver userId!");
+        }
+    }
+
+    private  WalletAccount createWalletAccount(String userName, double amountBalance) {
+        WalletAccount newAccount =  new WalletAccount(userName,amountBalance);
+        newAccount.getAccountStatement().add("created account with Balance: "+ amountBalance);
+        walletAccountList.add(newAccount);
+        return newAccount;
+    }
 
+    private void accountStatement(String userId){
+        WalletAccount account = null;
+        for (WalletAccount walletAccount : walletAccountList) {
+            if (walletAccount.getUserId().equals(userId)) {
+                account = walletAccount;
+                break;
+            }
+        }
+        if (account != null) {
+            System.out.println(account.getAccountStatement());
+        } else {
+            System.out.println("Couldn't find user Account with ID: " + userId);
+        }
+    }
 }
 

src/main/java/live/ashish/cpjava/systemdesign/wallet/WalletAccount.java

@@ -0,0 +1,22 @@
+package live.ashish.cpjava.systemdesign.wallet;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.UUID;
+
+@Data
+public class WalletAccount {
+    String userId;
+    String userName;
+    double amountBalance;
+    List<String> accountStatement = new ArrayList<>();
+
+    public WalletAccount(String userName, double amountBalance) {
+        this.userId = UUID.randomUUID().toString();
+        this.userName = userName;
+        this.amountBalance = amountBalance;
+    }
+}