How to create a get Method with nodes off a generic type in java

问题

I am implementing a cyclic DoublyLinkedList data structure. Like a singly linked list, nodes in a doubly linked list have a reference to the next node, but unlike a singly linked list, nodes in a doubly linked list also have a reference to the previous node.

Additionally, because the list is "cyclic", the "next" reference in the last node in the list points to the first node in the list, and the "prev" reference in the first node in the list points to the last node in the list.

I need help starting my get method, I've been looking around and I couldn't find anything that could help me since I am working with a Generic Type . I need to return E and every other examples show me it with int as an example. Here is my code:

public class DoublyLinkedList<E>
{
private Node first;
private int size;

@SuppressWarnings("unchecked")
public void add(E value)
{
    if (first == null)
    {
        first = new Node(value, null, null);
        first.next = first;
        first.prev = first;
    }
    else
        {
        first.prev.next = new Node(value, first, first.prev);
        first.prev = first.prev.next;
    }
    size++;
}
private class Node<E>
{
    private E data;
    private Node next;
    private Node prev;

    public Node(E data, Node next, Node prev)
    {
        this.data = data;
        this.next = next;
        this.prev = prev;
    }
}
@SuppressWarnings("unchecked")
public void add(int index, E value)
{
    if (first.data == null)
    {
        throw new IndexOutOfBoundsException();
    } else if (index == 0)
    {
        first = new Node(value, first.next, first.prev);
    }
    else
        {
        Node current = first;
        for (int i = 0; i < index - 1; i++)
        {
            current = current.next;
        }
        current.next = new Node(value, current.next, current.prev);
    }
}
@SuppressWarnings("unchecked")
public void remove(int index)
{
    if (first.data == null)
    {
        throw new IndexOutOfBoundsException();
    }
    else if (index == 0)
    {
        first = first.next;
    }
    else
        {
            Node current = first.next;
            for (int i = 0; i < index - 1; i++)
        {
            current = current.next;
        }
        current.next = current.next.next;
    }
    size--;
}

I can't think of a way to get started on this, but basically what this method should do is return the element at the specified index in the list. If the index parameter is invalid, an IndexOutOfBoundsException should be thrown.

public E get(int index)
{

}

Also, my remove method isn't accurate, but I'll figure that one out myself, I just need help with my get method.

回答1:

I figured it out, I'm just shocked that I wasn't getting any responses for this question. Either way, I am going to write some comments so it kind of guides future viewers who are struggling with this.

@SuppressWarnings("unchecked")
public E get(int index)
{
    if(index < 0) //The index needs to be above 0.
    {
        throw new IndexOutOfBoundsException(); 
    }
    if(index > size) //Since we're going to run a for loop, we need to make sure the index doesn't go past the size of the list. 
    {
        throw new IndexOutOfBoundsException();
    }
    Node current = first; //We want to create another node to perform this method.
    for (int i = 0; i < index; i++) //We are going to set i to 0 and loop around this for loop until we reach the index. 
    {
        current = current.next;
    }
    return (E) current.data; //Since we are working with generics, we need to return a type E, and it needs to be in parenthesis so it gets that object.
}

回答2:

Another problem I sort of had was that in my Node Class I had the in there, when I could've moved on without it. Lets update it to be

private class Node
{
    private E data;
    private Node next;
    private Node prev;

    public Node(E data, Node next, Node prev)
    {
        this.data = data;
        this.next = next;
        this.prev = prev;
    }
}

And now my getMethod() will be as follows:

@SuppressWarnings("unchecked")
public E get(int index)
{
    if(index < 0)
    {
        throw new IndexOutOfBoundsException();
    }
    if(index > size)
    {
        throw new IndexOutOfBoundsException();
    }
    Node current = first;
    for (int i = 0; i < index; i++)
    {
        current = current.next;
    }
    return current.data;
}

来源：https://stackoverflow.com/questions/55214062/how-to-create-a-get-method-with-nodes-off-a-generic-type-in-java