From 5f939afaf09cd7c0e7ca6011868cc30d24b00941 Mon Sep 17 00:00:00 2001
From: Azhwani <13301425+azhwani@users.noreply.github.com>
Date: Fri, 2 Dec 2022 18:50:50 +0100
Subject: [PATCH] BAEL-5931: Default Capacity of ArrayList (#13110)

---
 .../DefaultArrayListCapacity.java             | 20 +++++++++++
 .../DefaultArrayListCapacityUnitTest.java     | 33 +++++++++++++++++++
 2 files changed, 53 insertions(+)
 create mode 100644 core-java-modules/core-java-collections-array-list/src/main/java/com/baeldung/defaultarraylistcapacity/DefaultArrayListCapacity.java
 create mode 100644 core-java-modules/core-java-collections-array-list/src/test/java/com/baeldung/defaultarraylistcapacity/DefaultArrayListCapacityUnitTest.java

diff --git a/core-java-modules/core-java-collections-array-list/src/main/java/com/baeldung/defaultarraylistcapacity/DefaultArrayListCapacity.java b/core-java-modules/core-java-collections-array-list/src/main/java/com/baeldung/defaultarraylistcapacity/DefaultArrayListCapacity.java
new file mode 100644
index 0000000000..34f202a4dd
--- /dev/null
+++ b/core-java-modules/core-java-collections-array-list/src/main/java/com/baeldung/defaultarraylistcapacity/DefaultArrayListCapacity.java
@@ -0,0 +1,20 @@
+package com.baeldung.defaultarraylistcapacity;
+
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+
+public class DefaultArrayListCapacity {
+
+    public static int getDefaultCapacity(ArrayList<?> arrayList) throws Exception {
+
+        if (arrayList == null) {
+            return 0;
+        }
+
+        Field field = ArrayList.class.getDeclaredField("elementData");
+        field.setAccessible(true);
+
+        return ((Object[]) field.get(arrayList)).length;
+    }
+
+}
diff --git a/core-java-modules/core-java-collections-array-list/src/test/java/com/baeldung/defaultarraylistcapacity/DefaultArrayListCapacityUnitTest.java b/core-java-modules/core-java-collections-array-list/src/test/java/com/baeldung/defaultarraylistcapacity/DefaultArrayListCapacityUnitTest.java
new file mode 100644
index 0000000000..0690e93879
--- /dev/null
+++ b/core-java-modules/core-java-collections-array-list/src/test/java/com/baeldung/defaultarraylistcapacity/DefaultArrayListCapacityUnitTest.java
@@ -0,0 +1,33 @@
+package com.baeldung.defaultarraylistcapacity;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+
+import org.junit.jupiter.api.Test;
+
+public class DefaultArrayListCapacityUnitTest {
+
+    @Test
+    void givenEmptyArrayList_whenGetDefaultCapacity_thenReturnZero() throws Exception {
+
+        ArrayList<Integer> myList = new ArrayList<>();
+        int defaultCapacity = DefaultArrayListCapacity.getDefaultCapacity(myList);
+
+        assertEquals(0, defaultCapacity);
+
+    }
+
+    @Test
+    void givenEmptyArrayList_whenAddItemAndGetDefaultCapacity_thenReturn10() throws Exception {
+
+        ArrayList<String> myList = new ArrayList<>();
+        myList.add("ITEM 1");
+
+        int defaultCapacity = DefaultArrayListCapacity.getDefaultCapacity(myList);
+
+        assertEquals(10, defaultCapacity);
+
+    }
+
+}