feat: update structure

cs2030s/labs/Lab1/JoinShopQueueEvent.java

@@ -0,0 +1,24 @@
+
+class JoinShopQueueEvent extends Event {
+  private Customer customer;
+  private Shop shop;
+
+  public JoinShopQueueEvent(Customer customer, Shop shop) {
+    super(customer.getArrivalTIme());
+    this.customer = customer;
+    this.shop = shop;
+  }
+
+  @Override
+  public Event[] simulate() {
+    this.shop.joinQueue(customer);
+    return new Event[] {};
+  }
+
+  @Override
+  public String toString() {
+    return String.format("%s: %s joined shop queue %s",
+        super.toString(),
+        this.customer, this.shop);
+  }
+}