단방향 연결 목록

public final class BrokenNodeTraversalFailure {
    public static void main(String[] args) {
        Node first = new Node("node", new Node("link", null));
        Node current = first;
        for (int i = 0; i <= 2; i++) {
            current = current.next;
        }
        System.out.println(current.value);
    }

    private record Node(String value, Node next) {}
}

java.lang.NullPointerException

public final class LinkedNodeWalk {
    public static void main(String[] args) {
        NodeChain chain = new NodeChain();
        chain.add("node");
        chain.add("next");
        chain.add("head");
        System.out.println(chain.get(1));
        System.out.println(chain);
    }

    private static final class NodeChain {
        private Node head;
        private int size;

        void add(String value) {
            Node added = new Node(value);
            if (head == null) head = added;
            else getNode(size - 1).next = added;
            size++;
        }

        String get(int index) {
            check(index);
            return getNode(index).value;
        }

        private Node getNode(int index) {
            Node current = head;
            for (int i = 0; i < index; i++) {
                current = current.next;
            }
            return current;
        }

        private void check(int index) {
            if (index < 0 || index >= size) throw new IndexOutOfBoundsException(index);
        }

        public String toString() {
            StringBuilder out = new StringBuilder("[");
            for (Node current = head; current != null; current = current.next) {
                if (out.length() > 1) out.append(", ");
                out.append(current.value);
            }
            return out.append(']').toString();
        }
    }

    private static final class Node {
        String value;
        Node next;

        Node(String value) {
            this.value = value;
        }
    }
}

public final class PostRepositoryCliCH144 {
    public static void main(String[] args) {
        PostRepository repository = new PostRepository();
        repository.add("node-chain", 38);
        repository.add("linear-walk", 47);
        repository.print();
        System.out.println("total=" + repository.totalViewCount());
    }

    private static final class PostRepository {
        private Entry[] entries = new Entry[2];
        private int size;

        void add(String title, int viewCount) {
            if (title == null || title.isBlank()) throw new IllegalArgumentException("title");
            if (viewCount <= 0) throw new IllegalArgumentException("viewCount");
            ensureCapacity(size + 1);
            entries[size++] = new Entry(title, viewCount);
        }

        private void ensureCapacity(int required) {
            if (required <= entries.length) return;
            Entry[] grown = new Entry[Math.max(required, entries.length * 2)];
            System.arraycopy(entries, 0, grown, 0, size);
            entries = grown;
        }

        int totalViewCount() {
            int total = 0;
            for (int i = 0; i < size; i++) {
                total += entries[i].viewCount();
            }
            return total;
        }

        void print() {
            for (int i = 0; i < size; i++) {
                Entry entry = entries[i];
                System.out.println(i + ":" + entry.title() + "=" + entry.viewCount());
            }
        }
    }

    private record Entry(String title, int viewCount) {}
}