Bael 4215 creating generic array (#10178)

* Initial commit for generic arrays, using T[] and Object[]

* Add CollectionsList

* Create generic arrays example with a Stack

* Remove custom exception classes + throw RuntimeException instead.

core-java-modules/core-java-arrays-guides/src/main/java/com/baeldung/genericarrays/MyStack.java

@@ -0,0 +1,30 @@
+package com.baeldung.genericarrays;
+
+import java.lang.reflect.Array;
+
+public class MyStack<E> {
+    private E[] elements;
+    private int size = 0;
+
+    public MyStack(Class<E> clazz, int capacity) {
+        elements = (E[]) Array.newInstance(clazz, capacity);
+    }
+
+    public void push(E item) {
+        if (size == elements.length) {
+            throw new RuntimeException();
+        }
+        elements[size++] = item;
+    }
+
+    public E pop() {
+        if (size == 0) {
+            throw new RuntimeException();
+        }
+        return elements[--size];
+    }
+
+    public E[] getAllElements() {
+        return elements;
+    }
+}

core-java-modules/core-java-arrays-guides/src/test/java/com/baeldung/genericarrays/ListToArrayUnitTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.genericarrays;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class ListToArrayUnitTest {
+
+    @Test
+    public void givenListOfItems_whenToArray_thenReturnArrayOfItems() {
+        List<String> items = new LinkedList<>();
+        items.add("first item");
+        items.add("second item");
+
+        String[] itemsAsArray = items.toArray(new String[0]);
+
+        assertEquals("first item", itemsAsArray[0]);
+        assertEquals("second item", itemsAsArray[1]);
+    }
+}

core-java-modules/core-java-arrays-guides/src/test/java/com/baeldung/genericarrays/MyStackUnitTest.java

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+package com.baeldung.genericarrays;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class MyStackUnitTest {
+
+    @Test
+    public void givenStackWithTwoItems_whenPop_thenReturnLastAdded() {
+        MyStack<String> myStack = new MyStack<>(String.class, 2);
+        myStack.push("hello");
+        myStack.push("example");
+
+        assertEquals("example", myStack.pop());
+    }
+
+    @Test (expected = RuntimeException.class)
+    public void givenStackWithFixedCapacity_whenExceedCapacity_thenThrowException() {
+        MyStack<Integer> myStack = new MyStack<>(Integer.class, 2);
+        myStack.push(100);
+        myStack.push(200);
+        myStack.push(300);
+    }
+
+    @Test(expected = RuntimeException.class)
+    public void givenStack_whenPopOnEmptyStack_thenThrowException() {
+        MyStack<Integer> myStack = new MyStack<>(Integer.class, 1);
+        myStack.push(100);
+        myStack.pop();
+        myStack.pop();
+    }
+
+    @Test
+    public void givenStackWithItems_whenGetAllElements_thenSizeShouldEqualTotal() {
+        MyStack<String> myStack = new MyStack<>(String.class, 2);
+        myStack.push("hello");
+        myStack.push("example");
+
+        String[] items = myStack.getAllElements();
+
+        assertEquals(2, items.length);
+    }
+}