ArrayStack: Add stack implementation using array

Author: cszach

src/main/lists/ArrayStack.java

@@ -0,0 +1,50 @@
+/**
+ * An implementation of stack using static array.
+ *
+ * <p>
+ * Operations with their time complexities are:
+ *   <ul>
+ *     <li><code>push</code>: O(1)</li>
+ *     <li><code>pop</code>: O(1)</li>
+ *     <li><code>peek</code>: O(1)</li>
+ *   </ul>
+ *
+ */
+public class ArrayStack<T> {
+  private Object[] array;
+  private int length;
+
+  public ArrayStack(int capacity) {
+    this.array = new Object[capacity];
+    this.length = 0;
+  }
+
+  public int getLength() {
+    return this.length;
+  }
+
+  public int getCapacity() {
+    return this.array.length;
+  }
+
+  public ArrayStack<T> push(T data) {
+    if (this.length == this.array.length)
+      return this;
+
+    this.array[this.length++] = data;
+    return this;
+  }
+
+  public ArrayStack<T> pop() {
+    if (this.length == 0)
+      return this;
+
+    this.array[--this.length] = null;
+    return this;
+  }
+
+  @SuppressWarnings("unchecked")
+  public T peek() {
+    return (this.length == 0) ? null : (T) this.array[this.length - 1];
+  }
+}