自己實現一個泛型LinkedList

自己實現一個泛型LinkedList，保證最基本的 add(), remove(), get() , set(), 增強for循環等。

import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;

public class MyLinkedList<T> implements Iterable<T> {
    private int size;
    private int modCount = 0;
    private Node<T> beginMarker;
    private Node<T> endMarker;

    public MyLinkedList() {
        clear();
    }

    public void clear() {
        doClear();
    }

    private void doClear() {
        beginMarker = new Node<T>(null, null, null);
        endMarker = new Node<T>(null, beginMarker, null);
        beginMarker.next = endMarker;
        size = 0;
        modCount++;
    }

    public int size() {
        return size;
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public boolean add(T t) {
        addBefore(endMarker, t);
        return true;
    }

    public void add(int index, T t) {
        addBefore(getNode(index, 0, size), t);
    }

    public T get(int index) {
        return getNode(index).data;
    }

    public T set(int index, T t) {
        Node<T> p = getNode(index);
        T old = p.data;
        p.data = t;
        return old;
    }

    public T remove(int index) {
        return remove(getNode(index));
    }

    private T remove(Node<T> p) {
        p.prev.next = p.next;
        p.next.prev = p.prev;
        size--;
        modCount++;
        return p.data;
    }

    private void addBefore(Node<T> p, T t) {
        p.prev = p.prev.next = new Node<T>(t, p.prev, p);
        size++;
        modCount++;
    }

    private Node<T> getNode(int index) {
        return getNode(index, 0, size - 1);
    }

    private Node<T> getNode(int index, int lower, int upper) {
        if (index < lower || index > upper)
            throw new IndexOutOfBoundsException();
        Node<T> p;
        if (index < size / 2) {
            p = beginMarker.next;
            for (int i = 0; i < index; i++)
                p = p.next;
        } else {
            p = endMarker;
            for (int i = size; i > index; i--)
                p = p.prev;
        }
        return p;
    }

    @Override
    public String toString() {
        StringJoiner joiner = new StringJoiner(", ", "[", "]");
        Node<T> p = beginMarker.next;
        while (p != endMarker) {
            joiner.add(p.data.toString());
            p = p.next;
        }
        return joiner.toString();
    }

    @SuppressWarnings("all")
    private static class Node<T> {
        public T data;
        public Node<T> prev;
        public Node<T> next;

        public Node(T data, Node<T> prev, Node<T> next) {
            this.data = data;
            this.prev = prev;
            this.next = next;
        }
    }

    @Override
    public Iterator<T> iterator() {
        return new LinkedListIterator();
    }

    private class LinkedListIterator implements Iterator<T> {
        private Node<T> current = beginMarker.next;
        private int expectedModCount = modCount;
        private boolean okToRemove = false;

        @Override
        public boolean hasNext() {
            return current != endMarker;
        }

        @Override
        public T next() {
            if (expectedModCount != modCount)
                throw new ConcurrentModificationException();
            if (!hasNext())
                throw new NoSuchElementException();
            T data = current.data;
            current = current.next;
            okToRemove = true;
            return data;
        }

        public void remove() {
            if (expectedModCount != modCount)
                throw new ConcurrentModificationException();
            if (!okToRemove)
                throw new IllegalStateException();
            MyLinkedList.this.remove(current.prev);
            expectedModCount++;
            okToRemove = false;
        }
    }
}