org.apache.tapestry.ioc.util.Stack Maven / Gradle / Ivy

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// Copyright 2007 The Apache Software Foundation
//
// 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 org.apache.tapestry.ioc.util;

import org.apache.tapestry.ioc.internal.util.CollectionFactory;

/**
 * A simple, streamlined implementation of {@link java.util.Stack}. The implementation is
 * not threadsafe.
 *
 * @param 
 * the type of elements stored in the map
 * @see CollectionFactory#newStack()
 */
public class Stack
{
    private static final int MINIMUM_SIZE = 3;

    private static final int DEFAULT_ARRAY_SIZE = 20;

    private Object[] _items;

    private int _index = -1;

    /**
     * Normal constructor supporting an initial size of 20.
     */
    public Stack()
    {
        this(DEFAULT_ARRAY_SIZE);
    }

    /**
     * @param initialSize the initial size of the internal array (which will be expanded as necessary). For
     *                    best efficiency, set this to the maximum depth of the stack.
     */
    public Stack(int initialSize)
    {
        _items = new Object[Math.max(initialSize, MINIMUM_SIZE)];
    }

    /**
     * Returns true if the stack is empty.
     */
    public boolean isEmpty()
    {
        return _index < 0;
    }

    /**
     * Pushes a new item onto the stack.
     */
    public void push(E item)
    {
        _index++;

        if (_index == _items.length)
        {
            int newCapacity = (_items.length * 3) / 2 + 1;
            Object[] newItems = new Object[newCapacity];
            System.arraycopy(_items, 0, newItems, 0, _items.length);

            _items = newItems;
        }

        _items[_index] = item;
    }

    /**
     * Pops the top element off the stack and returns it.
     *
     * @return the top element of the stack
     * @throws IllegalStateException if the stack is empty
     */
    @SuppressWarnings("unchecked")
    public E pop()
    {
        checkIfEmpty();

        Object result = _items[_index];

        _items[_index] = null;

        _index--;

        return (E) result;
    }

    private void checkIfEmpty()
    {
        if (_index < 0) throw new IllegalStateException(UtilMessages.stackIsEmpty());
    }

    /**
     * Returns the top element of the stack without affecting the stack.
     *
     * @return top element on the stack
     * @throws IllegalStateException if the stack is empty
     */
    @SuppressWarnings("unchecked")
    public E peek()
    {
        checkIfEmpty();

        return (E) _items[_index];
    }

    /**
     * Describes the stack, listing the element in order of depth (top element first).
     *
     * @return string description of the stack
     */
    @Override
    public String toString()
    {
        StringBuilder builder = new StringBuilder("Stack[");

        for (int i = _index; i >= 0; i--)
        {
            if (i != _index) builder.append(", ");

            builder.append(String.valueOf(_items[i]));
        }

        builder.append("]");

        return builder.toString();
    }
}