Previous stack implementation bug fixed and queue implemented with singly linked list

Author: souravpalitrana

LinkedList/StackWithSinglyLinkedList/src/stackwithsinglylinkedlist/Queue.java

@@ -0,0 +1,78 @@
+/*
+ * To change this license header, choose License Headers in Project Properties.
+ * To change this template file, choose Tools | Templates
+ * and open the template in the editor.
+ */
+
+package stackwithsinglylinkedlist;
+
+import java.util.EmptyStackException;
+
+/**
+ *
+ * @author mac
+ */
+public class Queue <E> {
+     // Here we need head to traverse the linked list from starting to lastNode
+    private SinglyNode<E> head;
+    //Last node will help us to add a new value at the last with out moving the 
+    private SinglyNode<E> lastNode;
+    //Node count will track the length of the Queue
+    private int nodeCount = 0;
+
+   
+    /**
+     * Initializing head. First time both head and lastNode will be the same
+     * @param value 
+     */
+    private void add(E value) {
+        if(head == null) {
+            SinglyNode<E> node = new SinglyNode<>(null, value);
+            head = node;
+            lastNode = node;
+        } else {
+            SinglyNode<E> node = new SinglyNode<>(null, value);
+            lastNode.next = node;
+            lastNode = lastNode.next;
+        }
+        nodeCount++;
+    }
+    
+    public void removeFirst() {
+        head = head.next;
+        nodeCount--;
+    }
+    
+    public void push(E value) {
+        add(value);
+    }
+    
+    public void pop() {
+        if(nodeCount != 0) {
+            removeFirst();
+        }
+    }
+    
+    public E peek() throws EmptyStackException {
+        if(nodeCount > 0) {
+            return head.getItem();
+        } else {
+           
+            throw new EmptyStackException();
+        }
+    }
+    
+    public void display() {
+        if(head == null) return;
+        SinglyNode<E> tempNode = head;
+        
+        while(!tempNode.isLastNode()) {
+            System.out.println(tempNode.item);
+            tempNode = tempNode.getNext();
+        } 
+        // Printing the last item
+        System.out.println(tempNode.item);
+    }
+    
+}
+

LinkedList/StackWithSinglyLinkedList/src/stackwithsinglylinkedlist/Stack.java

@@ -13,11 +13,9 @@
  * @author SouravPalit
  */
 public class Stack<E> {
-     // Here we need head to traverse the linked list from starting to lastNode
+    
     private SinglyNode<E> head;
-    //Last node will help us to add a new value at the last with out moving the 
-    private SinglyNode<E> lastNode;
-    //Node count will track the length of the linked list
+    //Node count will track the length of the stack
     private int nodeCount = 0;
 
 
@@ -29,11 +27,11 @@ private void add(E value) {
         if(head == null) {
             SinglyNode<E> node = new SinglyNode<>(null, value);
             head = node;
-            lastNode = node;
         } else {
-            SinglyNode<E> node = new SinglyNode<>(null, value);
-            lastNode.next = node;
-            lastNode = lastNode.next;
+            SinglyNode<E> newNode = new SinglyNode<>(null, value);
+            SinglyNode<E> tempNode = head;
+            newNode.next = head;
+            head = newNode;
         }
         nodeCount++;
     }

LinkedList/StackWithSinglyLinkedList/src/stackwithsinglylinkedlist/StackWithSinglyLinkedList.java

@@ -18,6 +18,27 @@ public class StackWithSinglyLinkedList {
     public static void main(String[] args) {
         // TODO code application logic here
 
+        System.out.println("Printing Queue Values......");
+        
+        Queue<String> myQueue = new Queue<String>();
+        
+        myQueue.push("1");
+        myQueue.push("2");
+        myQueue.push("3");
+        myQueue.push("4");
+        myQueue.push("5");
+        
+        myQueue.pop();
+        
+        String value = myQueue.peek();
+        
+        System.out.println("Peek Value is = " + value);
+        
+        myQueue.display();
+        
+        
+        System.out.println("Printing Stack Values.....");
+        
         Stack<String> myStack = new Stack<String>();
 
         myStack.push("1");
@@ -28,7 +49,7 @@ public static void main(String[] args) {
 
         myStack.pop();
 
-        String value = myStack.peek();
+        value = myStack.peek();
 
         System.out.println("Peek Value is = " + value);