JDK1.7

JDK1.8

ArrayList (jdk1.7、jdk1.8)

数据结构

jdk1.7
//数据存储结构
private transient Object[] elementData;
jdk1.8
//数据存储结构
transient Object[] elementData;

默认容量

jdk1.7
public ArrayList() {
    this(10);
}
public ArrayList(int initialCapacity) {
    super();
    if (initialCapacity < 0)
        throw new IllegalArgumentException("Illegal Capacity: "+
                                           initialCapacity);
    this.elementData = new Object[initialCapacity];
}

jdk1.8
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
// size默认为0
private int size;
public ArrayList() {
    this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}

扩容

jdk1.7
public boolean add(E e) {
    // 扩容方法
    ensureCapacityInternal(size + 1);  
    elementData[size++] = e;
    return true;
}

private void ensureCapacityInternal(int minCapacity) {
    modCount++;
    // 大于当前数组长度才进行扩容
    if (minCapacity - elementData.length > 0)
        grow(minCapacity);
}
// 扩容正常最大值（-8因为java有保留）
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
// minCapacity-->add、addAll 方法计算需要最小容量
private void grow(int minCapacity) {
    int oldCapacity = elementData.length;
    // 新数组大小为原有数组1.5倍
    int newCapacity = oldCapacity + (oldCapacity >> 1);
    // 默认扩容大小、数组需要容量最小值 判断取最大值
    if (newCapacity - minCapacity < 0)
        newCapacity = minCapacity;
    if (newCapacity - MAX_ARRAY_SIZE > 0)
        newCapacity = hugeCapacity(minCapacity);
    // System.arraycopy native方法
    elementData = Arrays.copyOf(elementData, newCapacity);
}
// 获取数组长度最最最大值
private static int hugeCapacity(int minCapacity) {
    if (minCapacity < 0)
        throw new OutOfMemoryError();
    return (minCapacity > MAX_ARRAY_SIZE) ?
        Integer.MAX_VALUE :
        MAX_ARRAY_SIZE;
}


jdk1.8
// 默认扩容大小
private static final int DEFAULT_CAPACITY = 10;
public boolean add(E e) {
    // 扩容方法
    ensureCapacityInternal(size + 1);  
    elementData[size++] = e;
    return true;
}
//扩容内部方法
private void ensureCapacityInternal(int minCapacity) {
    // 对象为空{},本方法为第一次调用。比较默认容量和参数指定容量,取最大值
    if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
        // 最小长度为默认的10
        minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
    }

    ensureExplicitCapacity(minCapacity);
}
// 扩容判断方法
private void ensureExplicitCapacity(int minCapacity) {
    modCount++;

    // 大于数组长度才进行扩容
    if (minCapacity - elementData.length > 0)
        grow(minCapacity);
}
// 扩容正常最大值（-8因为java有保留）
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
//minCapacity-->add、addAll 方法计算需要最小容量
private void grow(int minCapacity) {
     int oldCapacity = elementData.length;
    // 新数组大小为原有数组1.5倍
    int newCapacity = oldCapacity + (oldCapacity >> 1);
     // 默认扩容大小、数组需要容量最小值 判断取最大值
    if (newCapacity - minCapacity < 0)
        newCapacity = minCapacity;
    if (newCapacity - MAX_ARRAY_SIZE > 0)
        newCapacity = hugeCapacity(minCapacity);
     // System.arraycopy native方法
    elementData = Arrays.copyOf(elementData, newCapacity);
}
// 获取数组长度最最最大值
private static int hugeCapacity(int minCapacity) {
    if (minCapacity < 0)
        throw new OutOfMemoryError();
    return (minCapacity > MAX_ARRAY_SIZE) ?
        Integer.MAX_VALUE :
        MAX_ARRAY_SIZE;
}

Vector (jdk1.7、jdk1.8)

数据结构

jdk1.7
  //数据结构
  protected Object[] elementData;
  // 容量增量
  protected int capacityIncrement;

jdk1.8
 // 数据结构
 protected Object[] elementData
  //容量增量
 protected int capacityIncrement;

默认容量

jdk1.7
// 默认10
public Vector() {
    this(10);
}
// 容量增量为0
public Vector(int initialCapacity) {
    this(initialCapacity, 0);
}
public Vector(int initialCapacity, int capacityIncrement) {
    super();
    if (initialCapacity < 0)
        throw new IllegalArgumentException("Illegal Capacity: "+
                                           initialCapacity);
    this.elementData = new Object[initialCapacity];
    this.capacityIncrement = capacityIncrement;
}

jdk1.8
// 同jdk1.7

扩容

jdk1.7
// 同步add方法
public synchronized boolean add(E e) {
    modCount++;
    ensureCapacityHelper(elementCount + 1);
    elementData[elementCount++] = e;
    return true;
}
// 扩容判断方法
private void ensureCapacityHelper(int minCapacity) {
    if (minCapacity - elementData.length > 0)
        grow(minCapacity);
}

private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
// 扩容方法
private void grow(int minCapacity) { 
    int oldCapacity = elementData.length;
    // 扩容增量大于0,按照指定的扩容增量增加,反之在原有长度上增加1倍
    int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
                                     capacityIncrement : oldCapacity);
    // 以下同ArrayList
    if (newCapacity - minCapacity < 0)
        newCapacity = minCapacity;
    if (newCapacity - MAX_ARRAY_SIZE > 0)
        newCapacity = hugeCapacity(minCapacity);
    elementData = Arrays.copyOf(elementData, newCapacity);
}

private static int hugeCapacity(int minCapacity) {
    if (minCapacity < 0) // overflow
        throw new OutOfMemoryError();
    return (minCapacity > MAX_ARRAY_SIZE) ?
        Integer.MAX_VALUE :
        MAX_ARRAY_SIZE;
}

jdk1.8
// 同jdk1.7

LinkedList (jdk1.7、jdk1.8)

数据结构

jdk1.7

transient int size = 0;
transient Node<E> first;// 第一个元素
transient Node<E> last;// 最后一个元素
private static class Node<E> {
    E item;//本身元素
    Node<E> next;// 下一个元素对象引用
    Node<E> prev;//上一个元素对象引用

    Node(Node<E> prev, E element, Node<E> next) {
        this.item = element;
        this.next = next;
        this.prev = prev;
    }
 }

 jdk1.8
 //同jdk1.7

默认容量

无默认容量(链表结构)

扩容

无需扩容,只要内存够大, 就可以无限制，前提是不考虑效率问题