Part I: insertFront in DList1 (1 point)

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Write a method called DList1.insertFront() that inserts an int at the front of

"this" DList1.

Part II: removeFront in DList1 (1 point)

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Write a method called DList1.removeFront() that removes the first item (and

node) from "this" DList1.

DList1.java

/* DList1.java */

/** * A DList1 is a mutable doubly-linked list. (No sentinel, not * circularly linked.) */

public class DList1 {

/** * head references the first node. * tail references the last node. * * DO NOT CHANGE THE FOLLOWING FIELD DECLARATIONS. */

protected DListNode1 head; protected DListNode1 tail; protected long size;

/* DList1 invariants: * 1) head.prev == null. * 2) tail.next == null. * 3) For any DListNode1 x in a DList, if x.next == y and x.next != null, * then y.prev == x. * 4) For any DListNode1 x in a DList, if x.prev == y and x.prev != null, * then y.next == x. * 5) The tail can be accessed from the head by a sequence of "next" * references. * 6) size is the number of DListNode1s that can be accessed from the * head by a sequence of "next" references. */

/** * DList1() constructor for an empty DList1. */ public DList1() { head = null; tail = null; size = 0; }

/** * DList1() constructor for a one-node DList1. */ public DList1(int a) { head = new DListNode1(); tail = head; head.item = a; size = 1; }

/** * DList1() constructor for a two-node DList1. */ public DList1(int a, int b) { head = new DListNode1(); head.item = a; tail = new DListNode1(); tail.item = b; head.next = tail; tail.prev = head; size = 2; }

/** * insertFront() inserts an item at the front of a DList1. */ public void insertFront(int i) { // Your solution here. }

/** * removeFront() removes the first item (and node) from a DList1. If the * list is empty, do nothing. */ public void removeFront() { // Your solution here. }

/** * toString() returns a String representation of this DList. * * DO NOT CHANGE THIS METHOD. * * @return a String representation of this DList. */ public String toString() { String result = "[ "; DListNode1 current = head; while (current != null) { result = result + current.item + " "; current = current.next; } return result + "]"; }

public static void main(String[] args) { // DO NOT CHANGE THE FOLLOWING CODE.

DList1 l = new DList1(); System.out.println("### TESTING insertFront ### Empty list is " + l);

l.insertFront(9); System.out.println(" Inserting 9 at front. List with 9 is " + l); if (l.head == null) { System.out.println("head is null."); } else { if (l.head.item != 9) { System.out.println("head.item is wrong."); } if (l.head.prev != null) { System.out.println("head.prev is wrong."); } } if (l.tail == null) { System.out.println("tail is null."); } else { if (l.tail.item != 9) { System.out.println("tail.item is wrong."); } if (l.tail.next != null) { System.out.println("tail.next is wrong."); } } if (l.size != 1) { System.out.println("size is wrong."); }

l.insertFront(8); System.out.println(" Inserting 8 at front. List with 8 and 9 is " + l); if (l.head == null) { System.out.println("head is null."); } else { if (l.head.item != 8) { System.out.println("head.item is wrong."); } if (l.head.prev != null) { System.out.println("head.prev is wrong."); } if (l.head.next != l.tail) { System.out.println("head.next is wrong."); } } if (l.tail == null) { System.out.println("tail is null."); } else { if (l.tail.item != 9) { System.out.println("tail.item is wrong."); } if (l.tail.next != null) { System.out.println("tail.next is wrong."); } if (l.tail.prev != l.head) { System.out.println("tail.prev is wrong."); } } if (l.size != 2) { System.out.println("size is wrong."); }

l = new DList1(1, 2); System.out.println(" ### TESTING removeFront ### List with 1 and 2 is " + l);

l.removeFront(); System.out.println(" Removing front node. List with 2 is " + l); if (l.head.item != 2) { System.out.println("head.item is wrong."); } if (l.head.prev != null) { System.out.println("head.prev is wrong."); } if (l.tail.item != 2) { System.out.println("tail.item is wrong."); } if (l.tail.next != null) { System.out.println("tail.next is wrong."); } if (l.size != 1) { System.out.println("size is wrong."); }

l.removeFront(); System.out.println(" Removing front node. Empty list is " + l); if (l.head != null) { System.out.println("head is wrong."); } if (l.tail != null) { System.out.println("tail is wrong."); } if (l.size != 0) { System.out.println("size is wrong."); }

l.removeFront(); System.out.println(" Removing front node. Empty list is " + l); if (l.head != null) { System.out.println("head is wrong."); } if (l.tail != null) { System.out.println("tail is wrong."); } if (l.size != 0) { System.out.println("size is wrong."); } }

}

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DlistNode1.java

/* DListNode1.java */

/** * A DListNode1 is a node in a DList1 (doubly-linked list). */

public class DListNode1 {

/** * item references the item stored in the current node. * prev references the previous node in the DList. * next references the next node in the DList. * * DO NOT CHANGE THE FOLLOWING FIELD DECLARATIONS. */

public int item; public DListNode1 prev; public DListNode1 next;

/** * DListNode1() constructor. */ DListNode1() { item = 0; prev = null; next = null; }

DListNode1(int i) { item = i; prev = null; next = null; } }

Thanks in advance