LinkedList Java implementation

Java/DoubleLinkedList.java

@@ -0,0 +1,37 @@
+
+public class DoubleLinkedList<T> implements LinkedList<T> {
+
+    private Node last = null;
+
+    private class Node {
+        private T item;
+        private Node next;
+        private Node previous;
+    }
+
+    public boolean isEmpty() {
+        return last == null;
+    }
+
+    public void push(final T item) {
+        Node oldLast = last;
+        last = new Node();
+        last.item = item;
+        last.previous = oldLast;
+        if (oldLast != null) {
+            oldLast.next = last;
+        }
+    }
+
+    public T pop() {
+        T item = null;
+        if (!isEmpty()) {
+            item = last.item;
+            last = last.previous;
+            if (last != null) {
+                last.next = null;
+            }
+        }
+        return item;
+    }
+}

Java/LinkedList.java

@@ -0,0 +1,8 @@
+
+public interface LinkedList<T> {
+
+    boolean isEmpty();
+    void push(T item);
+    T pop();
+
+}

Java/SingleLinkedList.java

@@ -0,0 +1,30 @@
+
+public class SingleLinkedList<T> implements LinkedList<T> {
+
+    private Node last = null;
+
+    private class Node {
+        private T item;
+        private Node previous;
+    }
+
+    public boolean isEmpty() {
+        return last == null;
+    }
+
+    public void push(final T item) {
+        Node oldLast = last;
+        last = new Node();
+        last.item = item;
+        last.previous = oldLast;
+    }
+
+    public T pop() {
+        T item = null;
+        if (!isEmpty()) {
+            item = last.item;
+            last = last.previous;
+        }
+        return item;
+    }
+}