18.2.3 ArrayList vs LinkedList性能对比

1. 数据结构基础

1.1 ArrayList底层实现

ArrayList基于动态数组实现，内部使用Object[]数组存储元素。

public class ArrayList<E> extends AbstractList<E> implements List<E> {
    
    // 默认初始容量
    private static final int DEFAULT_CAPACITY = 10;
    
    // 存储元素的数组
    transient Object[] elementData;
    
    // 实际元素数量
    private int size;
    
    // 构造方法
    public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }
    
    public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
            this.elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new IllegalArgumentException("Illegal Capacity: " + initialCapacity);
        }
    }
}

1.2 LinkedList底层实现

LinkedList基于双向链表实现，每个节点包含数据和前后指针。

public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E> {
    
    // 链表大小
    transient int size = 0;
    
    // 头节点
    transient Node<E> first;
    
    // 尾节点
    transient Node<E> last;
    
    // 节点结构
    private static class Node<E> {
        E item;
        Node<E> next;
        Node<E> prev;
        
        Node(Node<E> prev, E element, Node<E> next) {
            this.item = element;
            this.next = next;
            this.prev = prev;
        }
    }
    
    // 构造方法
    public LinkedList() {
    }
    
    public LinkedList(Collection<? extends E> c) {
        this();
        addAll(c);
    }
}

2. 核心操作性能分析

2.1 随机访问性能对比

ArrayList随机访问

public class ArrayListRandomAccess {
    
    // ArrayList的get方法 - O(1)
    public E get(int index) {
        rangeCheck(index);  // 边界检查
        return elementData(index);  // 直接数组访问
    }
    
    E elementData(int index) {
        return (E) elementData[index];
    }
    
    // 性能测试
    public void testRandomAccess() {
        ArrayList<Integer> arrayList = new ArrayList<>();
        
        // 添加10万个元素
        for (int i = 0; i < 100000; i++) {
            arrayList.add(i);
        }
        
        long startTime = System.nanoTime();
        
        // 随机访问1万次
        Random random = new Random();
        for (int i = 0; i < 10000; i++) {
            int index = random.nextInt(arrayList.size());
            Integer value = arrayList.get(index);
        }
        
        long endTime = System.nanoTime();
        System.out.println("ArrayList随机访问耗时: " + (endTime - startTime) / 1000000 + "ms");
    }
}

LinkedList随机访问

public class LinkedListRandomAccess {
    
    // LinkedList的get方法 - O(n)
    public E get(int index) {
        checkElementIndex(index);
        return node(index).item;
    }
    
    // 根据索引查找节点
    Node<E> node(int index) {
        // 优化：从距离较近的一端开始查找
        if (index < (size >> 1)) {
            Node<E> x = first;
            for (int i = 0; i < index; i++)
                x = x.next;
            return x;
        } else {
            Node<E> x = last;
            for (int i = size - 1; i > index; i--)
                x = x.prev;
            return x;
        }
    }
    
    // 性能测试
    public void testRandomAccess() {
        LinkedList<Integer> linkedList = new LinkedList<>();
        
        // 添加10万个元素
        for (int i = 0; i < 100000; i++) {
            linkedList.add(i);
        }
        
        long startTime = System.nanoTime();
        
        // 随机访问1万次
        Random random = new Random();
        for (int i = 0; i < 10000; i++) {
            int index = random.nextInt(linkedList.size());
            Integer value = linkedList.get(index);
        }
        
        long endTime = System.nanoTime();
        System.out.println("LinkedList随机访问耗时: " + (endTime - startTime) / 1000000 + "ms");
    }
}

2.2 插入操作性能对比

ArrayList插入操作

public class ArrayListInsert {
    
    // 尾部插入 - O(1) 均摊时间复杂度
    public boolean add(E e) {
        ensureCapacityInternal(size + 1);  // 确保容量
        elementData[size++] = e;
        return true;
    }
    
    // 指定位置插入 - O(n)
    public void add(int index, E element) {
        rangeCheckForAdd(index);
        ensureCapacityInternal(size + 1);
        
        // 移动元素
        System.arraycopy(elementData, index, elementData, index + 1, size - index);
        elementData[index] = element;
        size++;
    }
    
    // 扩容机制
    private void ensureCapacityInternal(int minCapacity) {
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
        }
        ensureExplicitCapacity(minCapacity);
    }
    
    private void ensureExplicitCapacity(int minCapacity) {
        modCount++;
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }
    
    private void grow(int minCapacity) {
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);  // 扩容1.5倍
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        
        elementData = Arrays.copyOf(elementData, newCapacity);
    }
    
    // 性能测试
    public void testInsertPerformance() {
        ArrayList<Integer> list = new ArrayList<>();
        
        // 测试尾部插入
        long startTime = System.nanoTime();
        for (int i = 0; i < 100000; i++) {
            list.add(i);
        }
        long endTime = System.nanoTime();
        System.out.println("ArrayList尾部插入耗时: " + (endTime - startTime) / 1000000 + "ms");
        
        // 测试头部插入
        list.clear();
        startTime = System.nanoTime();
        for (int i = 0; i < 10000; i++) {
            list.add(0, i);  // 头部插入
        }
        endTime = System.nanoTime();
        System.out.println("ArrayList头部插入耗时: " + (endTime - startTime) / 1000000 + "ms");
    }
}

LinkedList插入操作

public class LinkedListInsert {
    
    // 尾部插入 - O(1)
    public boolean add(E e) {
        linkLast(e);
        return true;
    }
    
    void linkLast(E e) {
        final Node<E> l = last;
        final Node<E> newNode = new Node<>(l, e, null);
        last = newNode;
        if (l == null)
            first = newNode;
        else
            l.next = newNode;
        size++;
        modCount++;
    }
    
    // 指定位置插入 - O(n)
    public void add(int index, E element) {
        checkPositionIndex(index);
        
        if (index == size)
            linkLast(element);
        else
            linkBefore(element, node(index));
    }
    
    void linkBefore(E e, Node<E> succ) {
        final Node<E> pred = succ.prev;
        final Node<E> newNode = new Node<>(pred, e, succ);
        succ.prev = newNode;
        if (pred == null)
            first = newNode;
        else
            pred.next = newNode;
        size++;
        modCount++;
    }
    
    // 头部插入 - O(1)
    public void addFirst(E e) {
        linkFirst(e);
    }
    
    private void linkFirst(E e) {
        final Node<E> f = first;
        final Node<E> newNode = new Node<>(null, e, f);
        first = newNode;
        if (f == null)
            last = newNode;
        else
            f.prev = newNode;
        size++;
        modCount++;
    }
    
    // 性能测试
    public void testInsertPerformance() {
        LinkedList<Integer> list = new LinkedList<>();
        
        // 测试尾部插入
        long startTime = System.nanoTime();
        for (int i = 0; i < 100000; i++) {
            list.add(i);
        }
        long endTime = System.nanoTime();
        System.out.println("LinkedList尾部插入耗时: " + (endTime - startTime) / 1000000 + "ms");
        
        // 测试头部插入
        list.clear();
        startTime = System.nanoTime();
        for (int i = 0; i < 100000; i++) {
            list.addFirst(i);  // 头部插入
        }
        endTime = System.nanoTime();
        System.out.println("LinkedList头部插入耗时: " + (endTime - startTime) / 1000000 + "ms");
    }
}

2.3 删除操作性能对比

ArrayList删除操作

public class ArrayListRemove {
    
    // 根据索引删除 - O(n)
    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; // 清除引用
        return oldValue;
    }
    
    // 根据对象删除 - O(n)
    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;
    }
    
    private void fastRemove(int index) {
        modCount++;
        int numMoved = size - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index, numMoved);
        elementData[--size] = null;
    }
    
    // 性能测试
    public void testRemovePerformance() {
        ArrayList<Integer> list = new ArrayList<>();
        
        // 准备数据
        for (int i = 0; i < 100000; i++) {
            list.add(i);
        }
        
        // 测试头部删除
        long startTime = System.nanoTime();
        for (int i = 0; i < 10000; i++) {
            if (!list.isEmpty()) {
                list.remove(0);  // 头部删除
            }
        }
        long endTime = System.nanoTime();
        System.out.println("ArrayList头部删除耗时: " + (endTime - startTime) / 1000000 + "ms");
    }
}

LinkedList删除操作

public class LinkedListRemove {
    
    // 根据索引删除 - O(n)
    public E remove(int index) {
        checkElementIndex(index);
        return unlink(node(index));
    }
    
    // 删除头部元素 - O(1)
    public E removeFirst() {
        final Node<E> f = first;
        if (f == null)
            throw new NoSuchElementException();
        return unlinkFirst(f);
    }
    
    private E unlinkFirst(Node<E> f) {
        final E element = f.item;
        final Node<E> next = f.next;
        f.item = null;
        f.next = null;
        first = next;
        if (next == null)
            last = null;
        else
            next.prev = null;
        size--;
        modCount++;
        return element;
    }
    
    // 删除节点
    E unlink(Node<E> x) {
        final E element = x.item;
        final Node<E> next = x.next;
        final Node<E> prev = x.prev;
        
        if (prev == null) {
            first = next;
        } else {
            prev.next = next;
            x.prev = null;
        }
        
        if (next == null) {
            last = prev;
        } else {
            next.prev = prev;
            x.next = null;
        }
        
        x.item = null;
        size--;
        modCount++;
        return element;
    }
    
    // 性能测试
    public void testRemovePerformance() {
        LinkedList<Integer> list = new LinkedList<>();
        
        // 准备数据
        for (int i = 0; i < 100000; i++) {
            list.add(i);
        }
        
        // 测试头部删除
        long startTime = System.nanoTime();
        for (int i = 0; i < 10000; i++) {
            if (!list.isEmpty()) {
                list.removeFirst();  // 头部删除
            }
        }
        long endTime = System.nanoTime();

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