int[] arr = {1, 2, 3};
List list = Arrays.asList(arr);
System.out.println(list.size());

public static List asList(T... a) {
    return new ArrayList<>(a);
}

List collect = Arrays.stream(arr).boxed().collect(Collectors.toList()); System.out.println(collect.size());
System.out.println(collect.get(0).getClass());
// 3
// class java.lang.Integer

Integer[] integerArr = {1, 2, 3};
List integerList = Arrays.asList(integerArr);
System.out.println(integerList.size()); System.out.println(integerList.get(0).getClass());
// 3
// class java.lang.Integer

private static void asListAdd(){
    String[] arr = {"1", "2", "3"};
    List<String> strings = new ArrayList<>(Arrays.asList(arr));
    arr[2] = "4";
    System.out.println(strings.toString());
    Iterator<String> iterator = strings.iterator();
    while (iterator.hasNext()){
        if ("4".equals(iterator.next())){
            iterator.remove();
        }
    }
    strings.forEach(val ->{
        strings.remove("4");
        strings.add("3");
    });


    System.out.println(Arrays.asList(arr).toString());
}

[1, 2, 4]
Exception in thread "main" java.lang.UnsupportedOperationException at java.util.AbstractList.remove(AbstractList.java:161) at java.util.AbstractList$Itr.remove(AbstractList.java:374) at java.util.AbstractCollection.remove(AbstractCollection.java:293) at JavaBase.List.AsListTest.lambda$asListAdd$0(AsListTest.java:47) at java.util.Arrays$ArrayList.forEach(Arrays.java:3880) at JavaBase.List.AsListTest.asListAdd(AsListTest.java:46) at JavaBase.List.AsListTest.main(AsListTest.java:20)

private static class ArrayList<E> extends AbstractList<E>
        implements RandomAccess, java.io.Serializable{
    private static final long serialVersionUID = -2764017481108945198L;
    private final E[] a;
    ArrayList(E[] array) {
        a = Objects.requireNonNull(array);
    }

    @Override
    public E get(int index) {}

    @Override
    public E set(int index, E element) {...}

...
}
public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {
    public boolean add(E e) {
        add(size(), e);
        return true;
    }
    public void add(int index, E element) {
        throw new UnsupportedOperationException();
    }

    public E remove(int index) {
        throw new UnsupportedOperationException();
    }

}

public static <T> List<T> asList(T... a) {
    return new ArrayList<>(a);
}
ArrayList(E[] array) {
    a = Objects.requireNonNull(array);
}

List strings = new ArrayList<>(Arrays.asList(arr));

private static void subListTest(){

    List<String> names = new ArrayList<String>() {{

    add("one");

    add("two");

    add("three");

}};
    ArrayList strings = (ArrayList) names.subList(0, 1);
    System.out.println(strings.toString());
}

Exception in thread "main" java.lang.ClassCastException: java.util.ArrayList$SubList cannot be cast to java.util.ArrayList

private class SubList extends AbstractList<E> implements RandomAccess {

    private final AbstractList<E> parent;
    private final int parentOffset;
    private final int offset;
    int size;
    SubList(AbstractList<E> parent,

    int offset, int fromIndex, int toIndex) {
    this.parent = parent;
    this.parentOffset = fromIndex;
    this.offset = offset + fromIndex;
    this.size = toIndex - fromIndex;
    this.modCount = ArrayList.this.modCount;
	}
}

List<String> names = new ArrayList<String>() {{
    add("one");
    add("two");
    add("three");
}};

List strings = names.subList(0, 1);

strings.add(0, "ongChange");

System.out.println(strings.toString());

System.out.println(names.toString());

[ongChange, one]

[ongChange, one, two, three]

List<String> names = new ArrayList<String>() {{

    add("one");
    add("two");
    add("three");

}};

List strings = names.subList(0, 1);

names.add("four");

System.out.println(strings.toString());

System.out.println(names.toString());

Exception in thread "main" java.util.ConcurrentModificationException

List strings = new ArrayList(names.subList(0, 1));

private static void subListOomTest(){
IntStream.range(0, 1000).forEach(i ->{
List<Integer> collect = IntStream.range(0, 100000).boxed().collect(Collectors.toList());
data.add(collect.subList(0, 1));
});
}}
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space

List list = new ArrayList<>(collect.subList(0, 1));

List list = collect.stream().skip(0).limit(1).collect(Collectors.toList());

private static void test(){
    StopWatch stopWatch = new StopWatch();
    int elementCount = 100000;
    stopWatch.start("ArrayList add");
    List<Integer> arrayList = IntStream.rangeClosed(1, elementCount).boxed().collect(Collectors.toCollection(ArrayList::new));
    // ArrayList插入數(shù)據(jù)
    IntStream.rangeClosed(0, elementCount).forEach(i ->arrayList.add(ThreadLocalRandom.current().nextInt(elementCount), 1));
    stopWatch.stop();

    stopWatch.start("linkedList add");
    List<Integer> linkedList = IntStream.rangeClosed(1, elementCount).boxed().collect(Collectors.toCollection(LinkedList::new));
    // ArrayList插入數(shù)據(jù)
    IntStream.rangeClosed(0, elementCount).forEach(i -> linkedList.add(ThreadLocalRandom.current().nextInt(elementCount), 1));
    stopWatch.stop();
    System.out.println(stopWatch.prettyPrint());
}

StopWatch '': running time = 44507882 ns
---------------------------------------------
ns % Task name
---------------------------------------------
043836412  098% elementCount 100 ArrayList add
000671470  002% elementCount 100 linkedList add

StopWatch '': running time = 196325261 ns
---------------------------------------------
ns % Task name
---------------------------------------------
053848980  027% elementCount 10000 ArrayList add
142476281  073% elementCount 10000 linkedList add

StopWatch '': running time = 26384216979 ns
---------------------------------------------
ns % Task name
---------------------------------------------
978501580  004% elementCount 100000 ArrayList add
25405715399  096% elementCount 100000 linkedList add

public void add(int index, E element) {

    checkPositionIndex(index);

    if (index == size)
        linkLast(element);
    else
        linkBefore(element, node(index));
}
    
/**
* Returns the (non-null) Node at the specified element index.
    */
Node<E> node(int index) {

    // assert isElementIndex(index);

    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;
    }
}

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++;
}

public boolean add(E e) {
    // 獲取獨占鎖
    final ReentrantLock lock = this.lock;
    lock.lock();
    try {
        // 獲取array
        Object[] elements = getArray();
        // 復(fù)制array到新數(shù)組，添加元素到新數(shù)組
        int len = elements.length;
        Object[] newElements = Arrays.copyOf(elements, len + 1);
        newElements[len] = e;
        // 替換數(shù)組
        setArray(newElements);
        return true;
    } finally {
        // 釋放鎖
        lock.unlock();
    }
}

public Iterator<E> iterator() {
    return new COWIterator<E>(getArray(), 0);
}

static final class COWIterator<E> implements ListIterator<E> {
    /** Snapshot of the array */
    private final Object[] snapshot;
    /** Index of element to be returned by subsequent call to next. */
    private int cursor;

    private COWIterator(Object[] elements, int initialCursor) {
        cursor = initialCursor;
        snapshot = elements;
    }

    public boolean hasNext() {
        return cursor < snapshot.length;
    }

    public boolean hasPrevious() {
        return cursor > 0;
    }

    @SuppressWarnings("unchecked")
    public E next() {
        if (! hasNext())
            throw new NoSuchElementException();
        return (E) snapshot[cursor++];
    }

private static void CopyOnWriteArrayListTest(){
    CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList();
    list.add("test1");
    list.add("test2");
    list.add("test3");
    list.add("test4");
    
    Thread thread = new Thread(() -> {
        System.out.println(">>>> start");
        list.add(1, "replaceTest");
        list.remove(2);
    });
    
    // 在啟動線程前獲取迭代器
    Iterator<String> iterator = list.iterator();

    thread.start();

    try {
        // 等待線程執(zhí)行完畢
        thread.join();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

    while (iterator.hasNext()){
        System.out.println(iterator.next());
    }
}

>>>> start
test1
test2
test3
test4

private static void CopyOnWriteArrayListTest(){
    CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
    list.add("test1");
    list.add("test2");
    list.add("test3");
    list.add("test4");

    Iterator<String> iterator = list.iterator();

    while (iterator.hasNext()){
        if ("test1".equals(iterator.next())){
            iterator.remove();
        }
    }

    System.out.println(list.toString());
}

Exception in thread "main" java.lang.UnsupportedOperationException
  at java.util.concurrent.CopyOnWriteArrayList$COWIterator.remove(CopyOnWriteArrayList.java:1178)

/**
 * Not supported. Always throws UnsupportedOperationException.
 * @throws UnsupportedOperationException always; {@code remove}
 * is not supported by this iterator.
 */
public void remove() {
    throw new UnsupportedOperationException();
}

/**
 * Not supported. Always throws UnsupportedOperationException.
 * @throws UnsupportedOperationException always; {@code set}
 * is not supported by this iterator.
 */
public void set(E e) {
    throw new UnsupportedOperationException();
}

/**
 * Not supported. Always throws UnsupportedOperationException.
 * @throws UnsupportedOperationException always; {@code add}
 * is not supported by this iterator.
 */
public void add(E e) {
    throw new UnsupportedOperationException();
}