| /** |
| * 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(); |
| } |
| } |