MemoryRefStack.java

/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed 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 com.smartandroid.sa.json;

import java.util.Stack;

import com.smartandroid.sa.json.internal.$Gson$Preconditions;

/**
 * A stack data structure that only does a memory reference comparison when
 * looking for a particular item in the stack. This stack does not allow
 * {@code null} values to be added.
 * 
 * @author Joel Leitch
 */
final class MemoryRefStack {
	private final Stack<ObjectTypePair> stack = new Stack<ObjectTypePair>();

	/**
	 * Adds a new element to the top of the stack.
	 * 
	 * @param obj
	 *            the object to add to the stack
	 * @return the object that was added
	 */
	public ObjectTypePair push(ObjectTypePair obj) {
		$Gson$Preconditions.checkNotNull(obj);
		return stack.push(obj);
	}

	/**
	 * Removes the top element from the stack.
	 * 
	 * @return the element being removed from the stack
	 * @throws java.util.EmptyStackException
	 *             thrown if the stack is empty
	 */
	public ObjectTypePair pop() {
		return stack.pop();
	}

	public boolean isEmpty() {
		return stack.isEmpty();
	}

	/**
	 * Retrieves the item from the top of the stack, but does not remove it.
	 * 
	 * @return the item from the top of the stack
	 * @throws java.util.EmptyStackException
	 *             thrown if the stack is empty
	 */
	public ObjectTypePair peek() {
		return stack.peek();
	}

	/**
	 * Performs a memory reference check to see it the {@code obj} exists in the
	 * stack.
	 * 
	 * @param obj
	 *            the object to search for in the stack
	 * @return true if this object is already in the stack otherwise false
	 */
	public boolean contains(ObjectTypePair obj) {
		if (obj == null) {
			return false;
		}

		for (ObjectTypePair stackObject : stack) {
			if (stackObject.getObject() == obj.getObject()
					&& stackObject.type.equals(obj.type)) {
				return true;
			}
		}
		return false;
	}
}