/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.fs.azure;
/**
* A simple generic stack implementation using linked lists. The stack
* implementation has five main operations:
* <ul>
* <li>push -- adds an element to the top of the stack</li>
* <li>pop -- removes an element from the top of the stack and returns a
* reference to it</li>
* <li>peek -- peek returns an element from the top of the stack without
* removing it</li>
* <li>isEmpty -- tests whether the stack is empty</li>
* <li>size -- returns the size of the stack</li>
* <li>toString -- returns a string representation of the stack.</li>
* </ul>
*/
public class AzureLinkedStack<E> {
/*
* Linked node for Azure stack collection.
*/
private static class AzureLinkedNode<E> {
private E element; // Linked element on the list.
private AzureLinkedNode<E> next;// Reference to the next linked element on
// list.
/*
* The constructor builds the linked node with no successor
*
* @param element : The value of the element to be stored with this node.
*/
private AzureLinkedNode(E anElement) {
element = anElement;
next = null;
}
/*
* Constructor builds a linked node with a specified successor. The
* successor may be null.
*
* @param anElement : new element to be created.
*
* @param nextElement: successor to the new element.
*/
private AzureLinkedNode(E anElement, AzureLinkedNode<E> nextElement) {
element = anElement;
next = nextElement;
}
/*
* Get the element stored in the linked node.
*
* @return E : element stored in linked node.
*/
private E getElement() {
return element;
}
/*
* Get the successor node to the element.
*
* @return E : reference to the succeeding node on the list.
*/
private AzureLinkedNode<E> getNext() {
return next;
}
}
private int count; // The number of elements stored on the stack.
private AzureLinkedNode<E> top; // Top of the stack.
/*
* Constructor creating an empty stack.
*/
public AzureLinkedStack() {
// Simply initialize the member variables.
//
count = 0;
top = null;
}
/*
* Adds an element to the top of the stack.
*
* @param element : element pushed to the top of the stack.
*/
public void push(E element) {
// Create a new node containing a reference to be placed on the stack.
// Set the next reference to the new node to point to the current top
// of the stack. Set the top reference to point to the new node. Finally
// increment the count of nodes on the stack.
//
AzureLinkedNode<E> newNode = new AzureLinkedNode<E>(element, top);
top = newNode;
count++;
}
/*
* Removes the element at the top of the stack and returns a reference to it.
*
* @return E : element popped from the top of the stack.
*
* @throws Exception on pop from an empty stack.
*/
public E pop() throws Exception {
// Make sure the stack is not empty. If it is empty, throw a StackEmpty
// exception.
//
if (isEmpty()) {
throw new Exception("AzureStackEmpty");
}
// Set a temporary reference equal to the element at the top of the stack,
// decrement the count of elements and return reference to the temporary.
//
E element = top.getElement();
top = top.getNext();
count--;
// Return the reference to the element that was at the top of the stack.
//
return element;
}
/*
* Return the top element of the stack without removing it.
*
* @return E
*
* @throws Exception on peek into an empty stack.
*/
public E peek() throws Exception {
// Make sure the stack is not empty. If it is empty, throw a StackEmpty
// exception.
//
if (isEmpty()) {
throw new Exception("AzureStackEmpty");
}
// Set a temporary reference equal to the element at the top of the stack
// and return the temporary.
//
E element = top.getElement();
return element;
}
/*
* Determines whether the stack is empty
*
* @return boolean true if the stack is empty and false otherwise.
*/
public boolean isEmpty() {
if (0 == size()) {
// Zero-sized stack so the stack is empty.
//
return true;
}
// The stack is not empty.
//
return false;
}
/*
* Determines the size of the stack
*
* @return int: Count of the number of elements in the stack.
*/
public int size() {
return count;
}
/*
* Returns a string representation of the stack.
*
* @return String String representation of all elements in the stack.
*/
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
AzureLinkedNode<E> current = top;
for (int i = 0; i < size(); i++) {
E element = current.getElement();
sb.append(element.toString());
current = current.getNext();
// Insert commas between strings except after the last string.
//
if (size() - 1 > i) {
sb.append(", ");
}
}
// Return the string.
//
return sb.toString();
}
}