1+ package lec16_inheritance4 ;
2+
3+ /* Represent a list of stuff, where all the "list" work is delegated
4+ * to a naked recursive data structure. */
5+
6+ public class SLList <Blorp > implements List61B <Blorp > {
7+ public class Node {
8+ public Blorp item ; /* Equivalent of first */
9+ public Node next ; /* Equivalent of rest */
10+
11+ public Node (Blorp i , Node h ) {
12+ item = i ;
13+ next = h ;
14+ }
15+ }
16+
17+ private Node sentinel ;
18+ private int size ;
19+
20+ /** Creates an empty list. */
21+ public SLList () {
22+ size = 0 ;
23+ sentinel = new Node (null , null );
24+ }
25+
26+ public SLList (Blorp x ) {
27+ size = 1 ;
28+ sentinel = new Node (null , null );
29+ sentinel .next = new Node (x , null );
30+ }
31+
32+ /** Adds an item of the front. */
33+ public void addFirst (Blorp x ) {
34+ Node oldFrontNode = sentinel .next ;
35+ Node newNode = new Node (x , oldFrontNode );
36+ sentinel .next = newNode ;
37+ size += 1 ;
38+ }
39+
40+ /** Gets the front item of the list. */
41+ public Blorp getFirst () {
42+ return sentinel .next .item ;
43+ }
44+
45+ /** Puts an item at the back of the list. */
46+ public void addLast (Blorp x ) {
47+ size += 1 ;
48+
49+ Node p = sentinel ;
50+
51+ /* Move p until it reaches the end. */
52+ while (p .next != null ) {
53+ p = p .next ;
54+ }
55+
56+ p .next = new Node (x , null );
57+ }
58+
59+ /** Returns the back node of our list. */
60+ private Node getLastNode () {
61+ Node p = sentinel ;
62+
63+ /* Move p until it reaches the end. */
64+ while (p .next != null ) {
65+ p = p .next ;
66+ }
67+ return p ;
68+ }
69+
70+ /** Returns last item */
71+ public Blorp getLast () {
72+ Node back = getLastNode ();
73+ return back .item ;
74+ }
75+
76+ /** Deletes and returns last item. */
77+ public Blorp removeLast () {
78+ Node back = getLastNode ();
79+ if (back == sentinel ) {
80+ return null ;
81+ }
82+
83+ size = size - 1 ;
84+ Node p = sentinel ;
85+
86+ while (p .next != back ) {
87+ p = p .next ;
88+ }
89+ p .next = null ;
90+ return back .item ;
91+ }
92+
93+ public int size () {
94+ return size ;
95+ }
96+
97+ /** Gets the positionth item of the list. */
98+ public Blorp get (int position ) {
99+ if (position == 0 ) {
100+ return getFirst ();
101+ }
102+ Node currentNode = sentinel .next .next ;
103+ while (position > 1 && currentNode .next != null ) {
104+ position -= 1 ;
105+ currentNode = currentNode .next ;
106+ }
107+
108+ return currentNode .item ;
109+ }
110+
111+ /** Inserts item into given position.
112+ * Code from discussion #3 */
113+ public void insert (Blorp item , int position ) {
114+ if (sentinel .next == null || position == 0 ) {
115+ addFirst (item );
116+ return ;
117+ }
118+
119+ Node currentNode = sentinel .next .next ;
120+ while (position > 1 && currentNode .next != null ) {
121+ position -= 1 ;
122+ currentNode = currentNode .next ;
123+ }
124+
125+ Node newNode = new Node (item , currentNode .next );
126+ currentNode .next = newNode ;
127+ }
128+
129+ /** TODO: Add a print method that overrides List61B's inefficient print method. */
130+
131+ }
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