156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson/* 256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * Copyright (C) 2010 Google Inc. 356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * 456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * Licensed under the Apache License, Version 2.0 (the "License"); 556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * you may not use this file except in compliance with the License. 656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * You may obtain a copy of the License at 756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * 856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * http://www.apache.org/licenses/LICENSE-2.0 956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * 1056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * Unless required by applicable law or agreed to in writing, software 1156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * distributed under the License is distributed on an "AS IS" BASIS, 1256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 1356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * See the License for the specific language governing permissions and 1456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * limitations under the License. 1556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson */ 1656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 1756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodsonpackage com.google.clearsilver.jsilver.data; 1856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 1956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodsonimport java.util.HashSet; 2056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodsonimport java.util.Iterator; 2156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodsonimport java.util.LinkedList; 2256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodsonimport java.util.NoSuchElementException; 2356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 2456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson/** 2556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * The {@code ResourceStack} represents a LIFO stack of unique objects (resources). 2656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * 2756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * <p> 2856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * An attempt to insert on a stack an object that is already there will fail and result with a 2956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * method {@link #push(Object)} returning false. 3056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * 3156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * <p> 3256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * All provided operations ({@link #pop()} and {@link #push(Object)}) are done in average constant 3356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * time. 3456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * 3556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * <p> 3656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * This class is iterable 3756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson */ 3856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodsonpublic class UniqueStack<T> implements Iterable<T> { 3956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson // Field used for optimization: when only one object was 4056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson // added we postpone the initialization and use this field. 4156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson private T firstObject = null; 4256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 4356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson // Contains a stack of all stored objects. 4456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson private LinkedList<T> objectStack = null; 4556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson // A HashSet allowing quick look-ups on the stack. 4656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson private HashSet<T> objectsSet = null; 4756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 4856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson /** 4956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * A wrapper for a {@code Iterator<T>} object that provides immutability. 5056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * 5156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * @param <T> 5256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson */ 5356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson private static class ImmutableIterator<T> implements Iterator<T> { 5456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson private static final String MODIFICATION_ERROR_MESSAGE = 5556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson "ResourceStack cannot be modyfied by Iterator.remove()"; 5656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 5756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson private final Iterator<T> iterator; 5856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 5956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson private ImmutableIterator(Iterator<T> iterator) { 6056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson this.iterator = iterator; 6156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 6256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 6356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson @Override 6456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson public boolean hasNext() { 6556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson return iterator.hasNext(); 6656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 6756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 6856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson @Override 6956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson public T next() { 7056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson return iterator.next(); 7156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 7256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 7356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson @Override 7456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson public void remove() { 7556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson throw new UnsupportedOperationException(MODIFICATION_ERROR_MESSAGE); 7656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 7756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 7856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 7956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson /** 8056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * Add an object to a stack. Object will be added only if it is not already on the stack. 8156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * 8256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * @param object to be added. If it is {@code null} a {@code NullPointerException} will be thrown. 8356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * @return true if the object was added successfully 8456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson */ 8556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson public boolean push(T object) { 8656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson if (object == null) { 8756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson throw new NullPointerException(); 8856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 8956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 9056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson if (objectStack == null) { 9156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson if (firstObject == null) { 9256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson firstObject = object; 9356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson return true; 9456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } else { 9556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson if (firstObject.equals(object)) { 9656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson return false; 9756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 9856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson initStackAndSet(); 9956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 10056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } else { 10156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson if (objectsSet.contains(object)) { 10256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson return false; 10356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 10456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 10556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 10656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson objectStack.offerLast(object); 10756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson objectsSet.add(object); 10856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson return true; 10956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 11056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 11156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson private void initStackAndSet() { 11256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson objectStack = new LinkedList<T>(); 11356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson objectsSet = new HashSet<T>(); 11456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 11556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson objectStack.offerLast(firstObject); 11656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson objectsSet.add(firstObject); 11756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 11856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson // there is no need for using firstObject pointer anymore 11956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson firstObject = null; 12056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 12156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 12256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson /** 12356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * Removes last added object from the stack. 12456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * 12556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * @return last added object 12656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * @throws NoSuchElementException - if the stack is empty 12756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson */ 12856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson public T pop() { 12956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson T returnedValue = null; 13056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 13156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson if (isEmpty()) { 13256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson throw new NoSuchElementException(); 13356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 13456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 13556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson if (objectStack == null) { 13656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson returnedValue = firstObject; 13756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson firstObject = null; 13856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } else { 13956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson returnedValue = objectStack.pollLast(); 14056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson objectsSet.remove(returnedValue); 14156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 14256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson return returnedValue; 14356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 14456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 14556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson /** 14656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * Returns {@code true} if this stack contains no elements. 14756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * 14856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson * @return {@code true} if this stack contains no elements. 14956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson */ 15056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson public boolean isEmpty() { 15156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson if (firstObject != null) { 15256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson return false; 15356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 15456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson return (objectStack == null || objectStack.isEmpty()); 15556ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 15656ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson 15756ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson @Override 15856ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson public Iterator<T> iterator() { 15956ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson if (objectStack == null) { 16056ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson initStackAndSet(); 16156ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 16256ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson return new ImmutableIterator<T>(objectStack.iterator()); 16356ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson } 16456ed4167b942ec265f9cee70ac4d71d10b3835ceBen Dodson} 165