Java中List的实现

源码来自JDK8

List接口

public interface List<E> extends Collection<E> { }

ArrayList

public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable{ private static final int DEFAULT_CAPACITY = 10; private static final Object[] EMPTY_ELEMENTDATA = {}; private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {}; transient Object[] elementData; public ArrayList() { this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA; } //新增元素 public boolean add(E e) { ensureCapacityInternal(size + 1); // Increments modCount!! elementData[size++] = e; return true; } //确保内部容量 private void ensureCapacityInternal(int minCapacity) { ensureExplicitCapacity(calculateCapacity(elementData, minCapacity)); } //计算所需容量 private static int calculateCapacity(Object[] elementData, int minCapacity) { if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) { return Math.max(DEFAULT_CAPACITY, minCapacity); } return minCapacity; } private void ensureExplicitCapacity(int minCapacity) { modCount++; // overflow-conscious code if (minCapacity - elementData.length > 0) grow(minCapacity); } //扩容并将数据复制到新数组中 //新容量 = 旧容量+旧容量/2 = 1.5个旧容量 private void grow(int minCapacity) { // overflow-conscious code int oldCapacity = elementData.length; int newCapacity = oldCapacity + (oldCapacity >> 1); if (newCapacity - minCapacity < 0) newCapacity = minCapacity; if (newCapacity - MAX_ARRAY_SIZE > 0) newCapacity = hugeCapacity(minCapacity); // minCapacity is usually close to size, so this is a win: 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; } }

LinkedList

public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, java.io.Serializable{ transient Node<E> first; transient Node<E> last; public LinkedList() { } }