https://jira.baeldung.com/browse/BAEL-9107 (#18289)

* https://jira.baeldung.com/browse/BAEL-9107

* https://jira.baeldung.com/browse/BAEL-9107

* https://jira.baeldung.com/browse/BAEL-9107

* https://jira.baeldung.com/browse/BAEL-9107

* https://jira.baeldung.com/browse/BAEL-9107

Author: Michaelin007

core-java-modules/core-java-collections-7/src/main/java/com/baeldung/customlinkedlist/CustomLinkedList.java

@@ -0,0 +1,120 @@
+package com.baeldung.customlinkedlist;
+
+public class CustomLinkedList<T> {
+    private Node<T> head;
+    private Node<T> tail;
+    private int size;
+
+    public CustomLinkedList() {
+        head = null;
+        tail = null;
+        size = 0;
+    }
+
+    public void insertTail(T value) {
+        if (size == 0) {
+            head = tail = new Node<>(value);
+        } else {
+            tail.next = new Node<>(value);
+            tail = tail.next;
+        }
+        size++;
+    }
+
+    public void insertHead(T value) {
+
+        Node<T> newNode = new Node<>(value);
+        newNode.next = head;
+        head = newNode;
+
+        if (size == 0) {
+            tail = newNode;
+        }
+
+        size++;
+    }
+
+    public T get(int index) {
+        if (index < 0 || index >= size) {
+            throw new IndexOutOfBoundsException("Index out of bounds");
+        }
+
+        Node<T> current = head;
+        for (int i = 0; i < index; i++) {
+            current = current.next;
+        }
+
+        return current.value;
+    }
+
+    public void removeHead() {
+        if (head == null)
+            return;
+        head = head.next;
+        if (head == null) {
+            tail = null;
+        }
+        size--;
+    }
+
+    public void removeTail() {
+        if (head == null) {
+            return;
+        }
+
+        if (head.next == null) {
+            head = null;
+            tail = null;
+        } else {
+            Node<T> current = head;
+            while (current.next != tail) {
+                current = current.next;
+            }
+            current.next = null;
+            tail = current;
+        }
+
+        size--;
+    }
+
+    public void removeAtIndex(int index) {
+        if (index < 0 || index >= size) {
+            throw new IndexOutOfBoundsException("Index out of bounds");
+        }
+
+        if (index == 0) {
+            removeHead();
+            return;
+        }
+
+        Node<T> current = head;
+        for (int i = 0; i < index - 1; i++) {
+            current = current.next;
+        }
+
+        if (current.next == tail) {
+            tail = current;
+        }
+
+        current.next = current.next.next;
+        size--;
+    }
+
+    public int size() {
+        return size;
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder builder = new StringBuilder();
+        Node<T> temp = head;
+        while (temp != null) {
+            builder.append(temp.value)
+                .append("->");
+            if (temp == tail)
+                builder.append("End");
+            temp = temp.next;
+        }
+        return builder.toString();
+    }
+}

core-java-modules/core-java-collections-7/src/main/java/com/baeldung/customlinkedlist/Node.java

@@ -0,0 +1,12 @@
+package com.baeldung.customlinkedlist;
+
+public class Node<T> {
+
+    T value;
+    Node<T> next;
+
+    public Node(T value) {
+        this.value = value;
+        this.next = null;
+    }
+}

core-java-modules/core-java-collections-7/src/test/java/com/baeldung/customlinkedlist/CustomLinkedListUnitTest.java

@@ -0,0 +1,66 @@
+package com.baeldung.customlinkedlist;
+
+import org.junit.Test;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class CustomLinkedListUnitTest {
+
+    @Test
+    public void givenLinkedList_whenBuildingReferenceBetweenNodes_thenCorrect() {
+        Node<Integer> node0 = new Node<>(1);
+        Node<Integer> node1 = new Node<>(2);
+        Node<Integer> node2 = new Node<>(3);
+        node0.next = node1;
+        node1.next = node2;
+
+        assertEquals(1, node0.value);
+        assertEquals(2, node0.next.value);
+        assertEquals(3, node0.next.next.value);
+    }
+
+    @Test
+    public void givenAnEmptyCustomLinkedList_whenInsertingNodes_thenReturnValueOfSpecifiedIndex() {
+        CustomLinkedList<String> fruit = new CustomLinkedList<>();
+        fruit.insertTail("Avocado");
+        fruit.insertTail("Banana");
+        fruit.insertTail("Apple");
+        assertEquals("Apple", fruit.get(2));
+    }
+
+    @Test
+    public void givenLinkedList_whenGettingElementByIndex_thenCorrect() {
+        CustomLinkedList<String> fruit = new CustomLinkedList<>();
+        fruit.insertTail("Avocado");
+        fruit.insertTail("Banana");
+        fruit.insertTail("Apple");
+        assertEquals("Avocado", fruit.get(0));
+    }
+
+    @Test
+    public void givenEmptyCustomLinkedList_whenInsertingElementAtTheHead_thenReturnCorrectSize() {
+        CustomLinkedList<String> fruit = new CustomLinkedList<>();
+        fruit.insertHead("Avocado");
+        fruit.insertHead("Banana");
+        fruit.insertHead("Apple");
+        assertEquals(3, fruit.size());
+    }
+
+    @Test
+    public void givenCustomLinkedList_whenRetrievingTheSizeOfTheList_thenCorrect() {
+        CustomLinkedList<String> fruit = new CustomLinkedList<>();
+        fruit.insertHead("Avocado");
+        fruit.insertHead("Banana");
+        fruit.insertHead("Apple");
+        assertEquals(3, fruit.size());
+    }
+
+    @Test
+    public void givenCustomLinkedList_whenRemovingANodeBaseOnIndex_thenReturnNewSize() {
+        CustomLinkedList<String> fruit = new CustomLinkedList<>();
+        fruit.insertHead("Avocado");
+        fruit.insertHead("Banana");
+        fruit.insertHead("Apple");
+        fruit.removeAtIndex(2);
+        assertEquals(2, fruit.size());
+    }
+}