linked list get first &last element?

Question

my program is about doubly linked list and I want to add two method one to get first element and another one to get last element ,these are my codes but when I add any code two this method it give me an error
package doublelinkeddd;
import java.util.NoSuchElementException;
public class DoublyLinkedListImpl<E> {
private Node head;
private Node tail;
private int size;

public DoublyLinkedListImpl() {
size = 0;
}

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

public Node(E element, Node next, Node prev) {
this.element = element;
this.next = next;
this.prev = prev;
}
}
public boolean isEmpty() { return size == 0; }

public E first(){

}
public E last(){

}
public void addFirst(E element) {
Node tmp = new Node(element, head, null);
if(head != null ) {head.prev = tmp;}
head = tmp;
if(tail == null) { tail = tmp;}
size++;
System.out.println("adding: "+element);
}

public static void main(String a[]){

DoublyLinkedListImpl<Integer> dll = new DoublyLinkedListImpl<Integer>();
dll.addFirst(10);
dll.addFirst(34);

}
}

husoski · Answer

That compiles just fine, except for the missing return statements in the first() and last() methods.

The only trick in coding those two is that you need to return a reference to an E type object.  If the list is empty, you'll either return null or throw an exception.  The first() method might look like:

E first() {
.... if (head==null) return null;
.... return head.element;
}

Change the "return null;" to an appropriate throw statement if you need an exception instead of a null result.  The last() method is nearly the same.

linked list get first &last element?

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