fix:lesson_16 bugs

Author: txtran224

lesson_16/objects/objects_app/src/main/java/com/codedifferently/lesson16/Coins.java renamed to lesson_16/objects/objects_app/src/main/java/com/codedifferently/lesson16/coins/Coins.java

@@ -1,4 +1,4 @@
-package com.codedifferently.lesson16;
+package com.codedifferently.lesson16.coins;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -58,7 +58,11 @@ public int getCoinAge() {
   }
 
   public List<String> getMaterial() {
-    return material;
+    List<String> materialsList = new ArrayList<>();
+    for (String mat : material) {
+      materialsList.add(mat);
+    }
+    return materialsList;
   }
 
   public static int convertNickelsToDimes(int totalNickels) {
@@ -68,7 +72,7 @@ public static int convertNickelsToDimes(int totalNickels) {
     return totalNickels / 2;
   }
 
-  public static List<Coins> CollectCoins() {
+  public static List<Coins> setCoinCollection() {
     Coins penny = new Coins(Coins.CoinType.PENNY, 1, true, 2.5, 1977, List.of("zinc", "copper"));
     Coins nickel =
         new Coins(Coins.CoinType.NICKEL, 5, true, 5.0, 1953, List.of("nickel", "copper"));

lesson_16/objects/objects_app/src/test/java/com/codedifferently/lesson16/CoinsTest.java renamed to lesson_16/objects/objects_app/src/test/java/com/codedifferently/lesson16/coins/CoinsTest.java

@@ -1,18 +1,15 @@
-package com.codedifferently.lesson16;
+package com.codedifferently.lesson16.coins;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import com.codedifferently.lesson16.coins.Coins.CoinType;
 import java.util.ArrayList;
 import java.util.List;
-
 import org.junit.jupiter.api.Test;
 
-import com.codedifferently.lesson16.Coins.CoinType;
-
 class CoinTest {
 
   @Test
@@ -55,16 +52,11 @@ void testConvertCoins() {
   }
 
   @Test
-  void testCollectCoins() {
+  void testCoinCollection() {
     // arrange
-    Coins.collectCoins();
-
-    List<Coins> coinCollection = Coins.getCoinCollection();
-
-    assertTrue(coinCollection.size() == 3);
-
-
+    List<Coins> coinCollection = Coins.setCoinCollection();
 
+    assertEquals(3, coinCollection.size());
   }
 
   @Test