用链表写一个字典

package structures.mapdemo;

public interface Map<K, V> {
    void add(K key, V value);
    V remove(K key);
    void set(K key, V newValue);
    V get(K key);
    int getSize();
    boolean isEmpty();
    boolean contains(K key);
}

package structures.mapdemo;

public class LinkedListMap<K, V> implements Map<K, V> {

    private class Node {
        public K key;
        public V value;
        public Node next;

        public Node(K key, V value, Node next) {
            this.key = key;
            this.value = value;
            this.next = next;
        }

        public Node() {
            this(null, null, null);
        }

        public Node(K key, V value) {
            this(key, value, null);
        }

        @Override
        public String toString() {
            return key + ":" + value;
        }
    }

    private Node dummyHead;
    private int size;

    public LinkedListMap() {
        dummyHead = new Node();
        size = 0;
    }

    private Node getNode(K key) {
        Node curNode = dummyHead.next;
        while (curNode != null) {
            if (curNode.key.equals(key)) {
                return curNode;
            }
            curNode = curNode.next;
        }
        return null;
    }

    @Override
    public void add(K key, V value) {
        Node node = getNode(key);
        if (node == null) {
            dummyHead.next = new Node(key, value, dummyHead.next);
        } else {
            node.value = value;
        }
        size++;
    }

    @Override
    public V remove(K key) {
        Node preNode = dummyHead;
        while (preNode.next != null) {
            if (preNode.next.key.equals(key)) {
                Node curNode = preNode.next;
                preNode.next = curNode.next;
                curNode.next = null;
                size --;
                return curNode.value;
            }
            preNode = preNode.next;
        }

        return null;
    }

    @Override
    public void set(K key, V newValue) {
        Node node = getNode(key);
        if (node != null) {
            node.value = newValue;
        } else {
            throw new IllegalArgumentException("Key is not here");
        }
    }

    @Override
    public V get(K key) {
        Node node = getNode(key);
        return node == null ? null : node.value;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    @Override
    public boolean contains(K key) {
        return getNode(key) != null;
    }

    @Override
    public String toString() {
        Node curNode = dummyHead.next;
        StringBuilder stringBuilder = new StringBuilder();
        while (curNode != null) {
            stringBuilder.append(curNode + "<-->");
            curNode = curNode.next;
        }
        return stringBuilder.toString();
    }
}