Update Exchange class with exceptions

src/main/java/Model/Exchange.java

@@ -17,20 +17,33 @@ public class Exchange {
     private final List<ExchangeObserver> observers = new ArrayList<>();
 
     public Exchange(String name, List<Stock> stocks) {
+        if (name == null || name.isBlank()) {
+            throw new IllegalArgumentException("Exchange name cannot be null or blank");
+        }
+        if (stocks == null) {
+            throw new IllegalArgumentException("Stock list cannot be null");
+        }
+
         this.name = name;
         this.week = 1;
         this.stockMap = new HashMap<>();
         this.random = new Random();
 
         for (Stock stock : stocks) {
+            if (stock == null) {
+                throw new IllegalArgumentException("Stock list must not contain null entries");
+            }
             stockMap.put(stock.getSymbol(), stock);
         }
     }
 
     // ---- Observer ----
 
     public void addObserver(ExchangeObserver observer) {
-        if (observer != null && !observers.contains(observer)) {
+        if (observer == null) {
+            throw new IllegalArgumentException("Observer cannot be null");
+        }
+        if (!observers.contains(observer)) {
             observers.add(observer);
         }
     }
@@ -54,14 +67,23 @@ public int getWeek() {
     }
 
     public boolean hasStock(String symbol) {
+        if (symbol == null || symbol.isBlank()) {
+            throw new IllegalArgumentException("Symbol cannot be null or blank");
+        }
         return stockMap.containsKey(symbol);
     }
 
     public Stock getStock(String symbol) {
+        if (symbol == null || symbol.isBlank()) {
+            throw new IllegalArgumentException("Symbol cannot be null or blank");
+        }
         return stockMap.get(symbol);
     }
 
     public List<Stock> findStocks(String searchTerm) {
+        if (searchTerm == null) {
+            throw new IllegalArgumentException("Search term cannot be null");
+        }
         List<Stock> result = new ArrayList<>();
         String lowerSearch = searchTerm.toLowerCase();
 
@@ -76,20 +98,27 @@ public List<Stock> findStocks(String searchTerm) {
         }
 
     public Transaction buy(String symbol, BigDecimal quantity, Player player) {
+        if (symbol == null || symbol.isBlank()) {
+            throw new IllegalArgumentException("Symbol cannot be null or blank");
+        }
+        if (quantity == null) {
+            throw new IllegalArgumentException("Quantity cannot be null");
+        }
+        if (quantity.compareTo(BigDecimal.ZERO) <= 0) {
+            throw new IllegalArgumentException("Quantity must be greater than zero");
+        }
+        if (player == null) {
+            throw new IllegalArgumentException("Player cannot be null");
+        }
+
         Stock stock = getStock(symbol);
-
-         // unngå nullpointerexception
         if (stock == null) {
-            return null; 
+            throw new IllegalArgumentException("No stock found with symbol: " + symbol);
         }
 
         // lager en ny "andel" basert på nåværende salgspris
         Share shareToBuy = new Share(stock, quantity, stock.getSalesPrice());
-
-        // oppretter kjøpstransaksjonen for den uka via fabrikken
-        Transaction purchase = TransactionFactory.createPurchase(shareToBuy, this.week);
-
-        // committer til player
+        Purchase purchase = new Purchase(shareToBuy, this.week);
         purchase.commit(player);
 
         notifyObservers();
@@ -98,15 +127,14 @@ public Transaction buy(String symbol, BigDecimal quantity, Player player) {
     }
 
     public Transaction sell(Share share, Player player) {
-        // unngå nullpointerexception
         if (share == null) {
-            return null;
+            throw new IllegalArgumentException("Share cannot be null");
+        }
+        if (player == null) {
+            throw new IllegalArgumentException("Player cannot be null");
         }
 
-        // oppretter salgstransaksjonen for den uka via fabrikken
-        Transaction sale = TransactionFactory.createSale(share, this.week);
-
-        // commiter til player
+        Sale sale = new Sale(share, this.week);
         sale.commit(player);
 
         notifyObservers();
@@ -138,14 +166,14 @@ public void advance() {
 
     public List<Stock> getGainers(int limit) { // viser "vinnerne"
         return stockMap.values().stream()
-            .sorted((stock1, stock2) -> stock2.getLatestPriceChange().compareTo(stock1.getLatestPriceChange())) 
+            .sorted((s1, s2) -> s2.getLatestPriceChange().compareTo(s1.getLatestPriceChange()))
             .limit(limit)
             .toList();
     }
 
     public List<Stock> getLosers(int limit) { // viser "taperne"
         return stockMap.values().stream()
-            .sorted((stock1, stock2) -> stock1.getLatestPriceChange().compareTo(stock2.getLatestPriceChange()))
+            .sorted((s1, s2) -> s1.getLatestPriceChange().compareTo(s2.getLatestPriceChange()))
             .limit(limit)
             .toList();
     }