Learned about Sets

Java Sets/src/ProductCatalogue.java

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+import common.Product;
+import common.Supplier;
+
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.Set;
+
+public class ProductCatalogue implements Iterable<Product> {
+    private final Set<Product> products = new HashSet<>();
+
+    public void addSupplier(final Supplier supplier) {
+
+        products.addAll(supplier.getProducts());
+    }
+
+    @Override
+    public Iterator<Product> iterator() {
+        return products.iterator();
+    }
+}

Java Sets/src/WeightAwareProductCatalogue.java

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+import common.Product;
+import common.Supplier;
+
+import java.util.Iterator;
+import java.util.NavigableSet;
+import java.util.Set;
+import java.util.TreeSet;
+
+public class WeightAwareProductCatalogue implements Iterable<Product> {
+    private final NavigableSet<Product> products =
+            new TreeSet<>(Product.BY_WEIGHT);
+
+    public void addSupplier(final Supplier supplier) {
+
+        products.addAll(supplier.getProducts());
+    }
+
+    public Set<Product> findLighterProducts(final Product product) {
+
+        return products.headSet(product, false);
+    }
+
+    @Override
+    public Iterator<Product> iterator() {
+
+        return products.iterator();
+    }
+}