【源码】List& AbstractList
java.util.List
package java.util;
import java.util.function.UnaryOperator;
public interface List<E> extends Collection<E> {
// Query Operations
int size();//集合的长度
boolean isEmpty();//集合是否为空
boolean contains(Object o);//集合是否包含传入的元素
Iterator<E> iterator();//集合对应的迭代器
Object[] toArray();//集合转换为数组
<T> T[] toArray(T[] a);//集合转换为数组（范型）
// Modification Operations
boolean add(E e);//在数组中添加此元素
boolean remove(Object o);//在数组中移除此元素
// Bulk Modification Operations批量修改操作
boolean containsAll(Collection<?> c);//集合属否包含指定集合的所有元素
boolean addAll(Collection<? extends E> c);//集合添加指定集合的所有元素
boolean addAll(int index, Collection<? extends E> c);//集合添加指定集合的所有元素，从下标index开始
boolean removeAll(Collection<?> c);//集合移除指定集合的所有元素
boolean retainAll(Collection<?> c);//集合移除指定集合的元素外的所有元素
//这个看下面的栗子
default void replaceAll(UnaryOperator<E> operator) {
Objects.requireNonNull(operator);
final ListIterator<E> li = this.listIterator();
while (li.hasNext()) {
li.set(operator.apply(li.next()));
}
}
//排序
@SuppressWarnings({"unchecked", "rawtypes"})
default void sort(Comparator<? super E> c) {
Object[] a = this.toArray();
Arrays.sort(a, (Comparator) c);
ListIterator<E> i = this.listIterator();
for (Object e : a) {
i.next();
i.set((E) e);
}
}
void clear();//清空集合
// Comparison and hashing
boolean equals(Object o);
int hashCode();
// Positional Access Operations
E get(int index);//获取指定下标index对应的元素
E set(int index, E element);//在指定下标index位置上插入指定元素element，并返回一个元素值
void add(int index, E element);//在指定下标index位置上插入指定元素element
E remove(int index);//移除指定下标index对应的元素
// Search Operations
int indexOf(Object o);//获取指定元素的下标
int lastIndexOf(Object o);//获取指定元素最后一个下标
// List Iterators
ListIterator<E> listIterator();
ListIterator<E> listIterator(int index);
// View
List<E> subList(int fromIndex, int toIndex);
//看下面的栗子
@Override
default Spliterator<E> spliterator() {
return Spliterators.spliterator(this, Spliterator.ORDERED);
}
}
java.util.AbstractList
package java.util;
public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {
/**
* Sole constructor. (For invocation by subclass constructors, typically
* implicit.)
*/
protected AbstractList() {
}
public boolean add(E e) {
add(size(), e);//size()正好是集合最后一个下标+1，在尾部添加新元素。
return true;
}
abstract public E get(int index);//子类实现
public E set(int index, E element) {//子类实现
throw new UnsupportedOperationException();
}
public void add(int index, E element) {//子类实现
throw new UnsupportedOperationException();
}
public E remove(int index) {//子类实现
throw new UnsupportedOperationException();
}
// Search Operations
//返回集合中等于元素o的第一个下标
public int indexOf(Object o) {
ListIterator<E> it = listIterator();
if (o==null) {
while (it.hasNext())
if (it.next()==null)
return it.previousIndex();
} else {
while (it.hasNext())
if (o.equals(it.next()))
return it.previousIndex();
}
return -1;
}
//返回集合中等于元素o的最后一个下标
public int lastIndexOf(Object o) {
ListIterator<E> it = listIterator(size());
if (o==null) {
while (it.hasPrevious())
if (it.previous()==null)
return it.nextIndex();
} else {
while (it.hasPrevious())
if (o.equals(it.previous()))
return it.nextIndex();
}
return -1;
}
// Bulk Operations
public void clear() {
removeRange(0, size());
}
public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index);
boolean modified = false;
for (E e : c) {
add(index++, e);//从index下标开始添加集合元素
modified = true;
}
return modified;
}
// Iterators
public Iterator<E> iterator() {
return new Itr();//返回Itr迭代器
}
public ListIterator<E> listIterator() {
return listIterator(0);
}
public ListIterator<E> listIterator(final int index) {
rangeCheckForAdd(index);
return new ListItr(index);//返回ListItr迭代器
}
private class Itr implements Iterator<E> {
int cursor = 0;//指针
/**
* Index of element returned by most recent call to next or
* previous. Reset to -1 if this element is deleted by a call
* to remove.
*/
int lastRet = -1;
/**
* The modCount value that the iterator believes that the backing
* List should have. If this expectation is violated, the iterator
* has detected concurrent modification.
*/
int expectedModCount = modCount;
public boolean hasNext() {
return cursor != size();
}
public E next() {
checkForComodification();
try {
int i = cursor;
E next = get(i);
lastRet = i;
cursor = i + 1;
return next;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
AbstractList.this.remove(lastRet);
if (lastRet < cursor)
cursor--;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException e) {
throw new ConcurrentModificationException();
}
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
private class ListItr extends Itr implements ListIterator<E> {
ListItr(int index) {
cursor = index;
}
public boolean hasPrevious() {
return cursor != 0;
}
public E previous() {
checkForComodification();
try {
int i = cursor - 1;
E previous = get(i);
lastRet = cursor = i;
return previous;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor-1;
}
public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
AbstractList.this.set(lastRet, e);
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void add(E e) {
checkForComodification();
try {
int i = cursor;
AbstractList.this.add(i, e);
lastRet = -1;
cursor = i + 1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
}
public List<E> subList(int fromIndex, int toIndex) {
return (this instanceof RandomAccess ?
new RandomAccessSubList<>(this, fromIndex, toIndex) :
new SubList<>(this, fromIndex, toIndex));
}
// Comparison and hashing
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof List))
return false;
ListIterator<E> e1 = listIterator();
ListIterator<?> e2 = ((List<?>) o).listIterator();
while (e1.hasNext() && e2.hasNext()) {
E o1 = e1.next();
Object o2 = e2.next();
if (!(o1==null ? o2==null : o1.equals(o2)))
return false;
}
return !(e1.hasNext() || e2.hasNext());
}
public int hashCode() {
int hashCode = 1;
for (E e : this)
hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
return hashCode;
}
protected void removeRange(int fromIndex, int toIndex) {
ListIterator<E> it = listIterator(fromIndex);
for (int i=0, n=toIndex-fromIndex; i<n; i++) {
it.next();
it.remove();
}
}
protected transient int modCount = 0;
private void rangeCheckForAdd(int index) {
if (index < 0 || index > size())
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size();
}
}
//视图
class SubList<E> extends AbstractList<E> {
private final AbstractList<E> l;
private final int offset;
private int size;
SubList(AbstractList<E> list, int fromIndex, int toIndex) {
if (fromIndex < 0)
throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
if (toIndex > list.size())
throw new IndexOutOfBoundsException("toIndex = " + toIndex);
if (fromIndex > toIndex)
throw new IllegalArgumentException("fromIndex(" + fromIndex +
") > toIndex(" + toIndex + ")");
l = list;//没有生成一个新集合，而是对原集合进行操作。
offset = fromIndex;
size = toIndex - fromIndex;
this.modCount = l.modCount;
}
public E set(int index, E element) {
rangeCheck(index);
checkForComodification();
return l.set(index+offset, element);
}
public E get(int index) {
rangeCheck(index);
checkForComodification();
return l.get(index+offset);
}
public int size() {
checkForComodification();
return size;
}
public void add(int index, E element) {
rangeCheckForAdd(index);
checkForComodification();
l.add(index+offset, element);
this.modCount = l.modCount;
size++;
}
public E remove(int index) {
rangeCheck(index);
checkForComodification();
E result = l.remove(index+offset);
this.modCount = l.modCount;
size--;
return result;
}
protected void removeRange(int fromIndex, int toIndex) {
checkForComodification();
l.removeRange(fromIndex+offset, toIndex+offset);
this.modCount = l.modCount;
size -= (toIndex-fromIndex);
}
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index);
int cSize = c.size();
if (cSize==0)
return false;
checkForComodification();
l.addAll(offset+index, c);
this.modCount = l.modCount;
size += cSize;
return true;
}
public Iterator<E> iterator() {
return listIterator();
}
public ListIterator<E> listIterator(final int index) {
checkForComodification();
rangeCheckForAdd(index);
return new ListIterator<E>() {
private final ListIterator<E> i = l.listIterator(index+offset);
public boolean hasNext() {
return nextIndex() < size;
}
public E next() {
if (hasNext())
return i.next();
else
throw new NoSuchElementException();
}
public boolean hasPrevious() {
return previousIndex() >= 0;
}
public E previous() {
if (hasPrevious())
return i.previous();
else
throw new NoSuchElementException();
}
public int nextIndex() {
return i.nextIndex() - offset;
}
public int previousIndex() {
return i.previousIndex() - offset;
}
public void remove() {
i.remove();
SubList.this.modCount = l.modCount;
size--;
}
public void set(E e) {
i.set(e);
}
public void add(E e) {
i.add(e);
SubList.this.modCount = l.modCount;
size++;
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
return new SubList<>(this, fromIndex, toIndex);
}
private void rangeCheck(int index) {
if (index < 0 || index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private void rangeCheckForAdd(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}
private void checkForComodification() {
if (this.modCount != l.modCount)
throw new ConcurrentModificationException();
}
}
class RandomAccessSubList<E> extends SubList<E> implements RandomAccess {
RandomAccessSubList(AbstractList<E> list, int fromIndex, int toIndex) {
super(list, fromIndex, toIndex);
}
public List<E> subList(int fromIndex, int toIndex) {
return new RandomAccessSubList<>(this, fromIndex, toIndex);
}
}
栗子
package com.yaochow.demo;
import java.util.*;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ListTest {
private static List<Integer> TEST_LIST = new ArrayList<>();
private static Spliterator<Integer> spliterator;
public static void main(String[] args) throws InterruptedException {
initArray();
spliterator = TEST_LIST.spliterator();
ExecutorService executorService = Executors.newFixedThreadPool(5);
final Map<String, List<Integer>> countMap = new HashMap<>();
final CountDownLatch countDownLatch = new CountDownLatch(5);
for (int i = 0; i < 5; i++) {
executorService.execute(() -> {
countMap.put(Thread.currentThread().getName(), new ArrayList<>());
Spliterator<Integer> integerSpliterator = spliterator.trySplit();
integerSpliterator.forEachRemaining(
integer -> countMap.get(Thread.currentThread().getName()).add(integer));
countDownLatch.countDown();
});
}
countDownLatch.await();
executorService.shutdown();
countMap.put(Thread.currentThread().getName(), new ArrayList<>());
spliterator.forEachRemaining(
integer -> countMap.get(Thread.currentThread().getName()).add(integer));
countMap.entrySet().forEach(value -> {
value.getValue().replaceAll(t -> t + 1);
System.out.println("thread-name:【" + value.getKey() + "】, execute: 【" + Arrays.toString(value.getValue().toArray()) + "】");
});
}
private static void initArray() {
for (int i = 0; i < 100; i++)
TEST_LIST.add(i);
}
}
执行结果：
thread-name:【pool-1-thread-1】, execute: 【[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50]】
thread-name:【pool-1-thread-3】, execute: 【[76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87]】
thread-name:【pool-1-thread-2】, execute: 【[51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75]】
thread-name:【pool-1-thread-5】, execute: 【[94, 95, 96]】
thread-name:【pool-1-thread-4】, execute: 【[88, 89, 90, 91, 92, 93]】
thread-name:【main】, execute: 【[97, 98, 99, 100]】
- 栗子中先初始化一个集合，从0～99共100个元素。
- 通过线程池启动5个线程，每个线程中会将所执行的数据放到map中。
- 最后打印出map中统计的数据
栗子中使用到了CountDownLatch是为了可以最后完整的打印出结果，CountDownLatch可以使一个线程等待其他线程完成后继续执行。
从打印结果中能看出replaceAll方法将集合中原有元素都加了1 (t-> t+1)。
至于spliterator方法将集合分为了几块，每个线程分别去执行不同的分块，这样可以保证线程安全。从打印结果中可以看出，第一个线程执行了50个，第二个25，第三个12，第四个6，第五个3，剩下的由主线程完成的。 也就是说每次都进行二等分分给新的线程来执行。最后的部分应不去调用trySplit方法，而是直接调用forEachRemaining，保证所有的数据都执行完整。
总结
- List是一个有序集合，继承自java.util.Collection。
- AbstractList继承AbstractCollection实现List接口。
- 相比java.util.Collection增加了一些与索引相关的方法定义。
- List中每个元素都对应着一个索引，允许有重复元素。
- jdk1.8增加了spliterator等新特性。
源码中大部分都标了注释，有些特别简单的就没有加； jdk1.8新增的方法写在了栗子中。
- 以上源码来自JDK1.8.0_171