import java.util.ArrayList;

public class testCompareArrayAndList {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		
		ArrayList<Integer> arrayList = new ArrayList<Integer>();
		//添加元素
		for(int i =0;i< 11999999;i++){
			arrayList.add(i);
		}		
		//list => array
		Integer[] array = arrayList.toArray(new Integer[arrayList.size()]);
		
		long currentTimeMillis1 = System.currentTimeMillis();
		for(Integer i :array){}
		long currentTimeMillis2 = System.currentTimeMillis();
		System.out.println("遍历数组耗费时间： "+(currentTimeMillis2 - currentTimeMillis1)+" ms");
		
		currentTimeMillis1 = System.currentTimeMillis();
		for(Integer i : arrayList){}
		currentTimeMillis2 = System.currentTimeMillis();
		System.out.println("遍历列表耗费时间： "+(currentTimeMillis2 - currentTimeMillis1)+" ms");

	}

}

console：

遍历数组耗费时间： 2 ms
遍历列表耗费时间： 39 ms

性能分析

1）数组Array：

参考文章：《java数组详解》

2）列表ArrayList：

2.1 构造函数

一、初始化设置容量

/**
* Constructs an empty list with the specified initial capacity.
*
* @param initialCapacity the initial capacity of the list
* @throws IllegalArgumentException if the specified initial capacity
* is negative
*/

    public ArrayList(int initialCapacity) {
        super();
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        this.elementData = new Object[initialCapacity];
    }

二、无参构造函数

/**
* Constructs an empty list with an initial capacity of ten.
*/

   public ArrayList() {
        super();
        this.elementData = EMPTY_ELEMENTDATA;
    }

三、初始化元素

/**
* Constructs a list containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param c the collection whose elements are to be placed into this list
* @throws NullPointerException if the specified collection is null
*/

   public ArrayList(Collection<? extends E> c) {
        elementData = c.toArray();
        size = elementData.length;
        // c.toArray might (incorrectly) not return Object[] (see 6260652)
        if (elementData.getClass() != Object[].class)
            elementData = Arrays.copyOf(elementData, size, Object[].class);
    }

2.2 成员变量

    private static final long serialVersionUID = 8683452581122892189L;

    /**
     * Default initial capacity.
     */
    private static final int DEFAULT_CAPACITY = 10;

    /**
     * Shared empty array instance used for empty instances.
     */
    private static final Object[] EMPTY_ELEMENTDATA = {};

    /**
     * The array buffer into which the elements of the ArrayList are stored.
     * The capacity of the ArrayList is the length of this array buffer. Any
     * empty ArrayList with elementData == EMPTY_ELEMENTDATA will be expanded to
     * DEFAULT_CAPACITY when the first element is added.
     */
    private transient Object[] elementData;

    /**
     * The size of the ArrayList (the number of elements it contains).
     *
     * @serial
     */
    private int size;

1）elementData ：内存实际保存元素是一个数组，即ArrayList是对数组的一个封装；

2）size：ArrayList的实际长度；

2.3 add 方法（队列末尾插入一个元素 / 队列特定位置插入一个元素）

/**
* Appends the specified element to the end of this list.
*
* @param e element to be appended to this list
* @return <tt>true</tt> (as specified by {@link Collection#add})
*/

    public boolean add(E e) {
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }

/**
* Inserts the specified element at the specified position in this
* list. Shifts the element currently at that position (if any) and
* any subsequent elements to the right (adds one to their indices).
*
* @param index index at which the specified element is to be inserted
* @param element element to be inserted
* @throws IndexOutOfBoundsException {@inheritDoc}
*/

    public void add(int index, E element) {
        rangeCheckForAdd(index);

        ensureCapacityInternal(size + 1);  // Increments modCount!!
        System.arraycopy(elementData, index, elementData, index + 1,
                         size - index);
        elementData[index] = element;
        size++;
    }

2.4 remove方法（删除指定位置的元素 / 删除某个元素）

/**
* Removes the element at the specified position in this list.
* Shifts any subsequent elements to the left (subtracts one from their
* indices).
*
* @param index the index of the element to be removed
* @return the element that was removed from the list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/

    public E remove(int index) {
        rangeCheck(index);

        modCount++;
        E oldValue = elementData(index);

        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index,
                             numMoved);
        elementData[--size] = null; // clear to let GC do its work

        return oldValue;
    }

/**
* Removes the first occurrence of the specified element from this list,
* if it is present. If the list does not contain the element, it is
* unchanged. More formally, removes the element with the lowest index
* <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
* (if such an element exists). Returns <tt>true</tt> if this list
* contained the specified element (or equivalently, if this list
* changed as a result of the call).
*
* @param o element to be removed from this list, if present
* @return <tt>true</tt> if this list contained the specified element
*/

    public boolean remove(Object o) {
        if (o == null) {
            for (int index = 0; index < size; index++)
                if (elementData[index] == null) {
                    fastRemove(index);
                    return true;
                }
        } else {
            for (int index = 0; index < size; index++)
                if (o.equals(elementData[index])) {
                    fastRemove(index);
                    return true;
                }
        }
        return false;
    }

2.5 get 方法


    @SuppressWarnings("unchecked")
    E elementData(int index) {
        return (E) elementData[index];
    }

    /**
     * Returns the element at the specified position in this list.
     *
     * @param  index index of the element to return
     * @return the element at the specified position in this list
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public E get(int index) {
        rangeCheck(index);

        return elementData(index);
    }

实际返回的是数组的某个元素。

以上是对源码的一些走读总结。

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