Implement Doubly LinkedList and test the correctness of your program.

1. UML class diagram of class DNode

DNode

element: Object

prev: DNode

next: DNode

+ DNode(Object element, DNode prev, DNode next)

+ getElement(): Object

+ getPrev(): DNode

+ getNext(): DNode

+ setElement(Object element): void

+ setPrev(DNode prev): void

+ setNext(DNode next): void

2. UML class diagram of class DList

DList

header: DNode

trailer: DNode

+ DList()

+ getHeader(): DNode

+ getTrailer(): DNode

+ setHeader(DNode header): void

+ setTrailer(DNode trailer): void

+ print(): void // output all elements in DList

+ addFirst(DNode n): void // add the node n after header

+ addLast(DNode n): void // add the node n before trailer

+ remove(DNode n): void // remove the node n

+ reverse(): void // reverse the Doubly LinkedList

+ main(String[] args): void // test

3. Testing cases:

Create DNodes a (element = 1), b (element = 2), c (element = 3)

Create DList d

Print all elements in d // output nothing

Call addFirst to add b to d; Call addFirst to add a to d; Call addLast to add c to d; then print all elements in d // output 1, 2, 3

Remove b, and then print all elements in d // output 1, 3

Remove a, and then print all elements in d // output 3

Remove c, and then print all elements in d // output nothing

Call addFirst to add b to d; Call addFirst to add a to d; Call addLast to add c to d; then print all elements in d // output 1, 2, 3

Reverse d, and then print all elements in d // output 3, 2, 1

4. Add more features to class DList, and design testing cases to test them by yourself (you may need them for future project).

Add a method in DList to search whether it contains an element x

Add a method in DList to return the index i of element x

Add a method in DList to add a node at index i

Add a method in DList to remove the node at index i