stack interface + implementation

Author: Ram swaroop

src/me/ramswaroop/common/LinkedStack.java

@@ -0,0 +1,93 @@
+package me.ramswaroop.common;
+
+import me.ramswaroop.interfaces.Stack;
+
+import java.util.NoSuchElementException;
+
+/**
+ * Created by IntelliJ IDEA.
+ * User: ramswaroop
+ * Date: 3/24/15
+ * Time: 3:02 PM
+ * To change this template go to Preferences | IDE Settings | File and Code Templates
+ */
+
+/**
+ * Stack implementation using
+ * a singly linked list
+ *
+ * @param <E>
+ */
+public class LinkedStack<E> implements Stack<E> {
+
+    private Node top = null;
+
+    /**
+     * Pushes an item onto the top of this stack.
+     *
+     * @param item
+     */
+    @Override
+    public void push(E item) {
+        top = new Node(item, top);
+    }
+
+    /**
+     * Removes the object at the top of this stack and returns that object as the value of this function.
+     *
+     * @return
+     */
+    @Override
+    public E pop() {
+        E item = peek();
+        top = top.next;
+        return item;
+    }
+
+    /**
+     * Looks at the object at the top of this stack without removing it from the stack.
+     *
+     * @return
+     */
+    @Override
+    public E peek() {
+        if (top == null) {
+            throw new NoSuchElementException();
+        }
+        return top.data;
+    }
+
+    /**
+     * Returns the number of items currently in the stack.
+     *
+     * @return
+     */
+    @Override
+    public int size() {
+        int count = 0;
+        for (Node node = top; node != null; node = top.next) {
+            count++;
+        }
+        return count;
+    }
+
+    /**
+     * Tests if this stack is empty.
+     *
+     * @return
+     */
+    @Override
+    public boolean isEmpty() {
+        return top == null;
+    }
+
+    private class Node {
+        E data;
+        Node next;
+
+        Node(E data, Node next) {
+            this.data = data;
+            this.next = next;
+        }
+    }
+}

src/me/ramswaroop/common/Stack.java

@@ -0,0 +1,45 @@
+package me.ramswaroop.interfaces;
+
+/**
+ * Created by IntelliJ IDEA.
+ * User: ramswaroop
+ * Date: 4/3/15
+ * Time: 9:47 AM
+ * To change this template go to Preferences | IDE Settings | File and Code Templates
+ */
+public interface Stack<E> {
+    /**
+     * Pushes an item onto the top of this stack.
+     *
+     * @param item
+     */
+    public void push(E item);
+
+    /**
+     * Removes the object at the top of this stack and returns that object as the value of this function.
+     *
+     * @return
+     */
+    public E pop();
+
+    /**
+     * Looks at the object at the top of this stack without removing it from the stack.
+     *
+     * @return
+     */
+    public E peek();
+
+    /**
+     * Returns the number of items currently in the stack.
+     *
+     * @return
+     */
+    public int size();
+
+    /**
+     * Tests if this stack is empty.
+     *
+     * @return
+     */
+    public boolean isEmpty();
+}