hashmap原理面试回答

HashMap是一种散列表，它存储的内容是键值对(key-value)映射。当我们将一个键值对存储在HashMap中时，它会根据键的哈希码找到对应的桶(bucket)，然后将键值对存储在桶中。当我们需要获取一个键对应的值时，HashMap会根据键的哈希码找到对应的桶，然后在桶中查找对应的值。

在面试中，如果被问到HashMap是否有序，我们需要回答说HashMap不是有序的，因为HashMap中的键值对是根据哈希码存储的，而哈希码是无序的。如果被问到HashMap的存储原理，我们需要回答说HashMap是通过哈希算法将键映射到桶中的，然后将键值对存储在桶中。如果被问到哈希算法的底层实现，我们需要回答说哈希算法的底层实现是哈希表。

以下是一个简单的HashMap的实现代码，仅供参考：

public class MyHashMap<K, V> {
    private static final int DEFAULT_CAPACITY = 16;
    private static final float DEFAULT_LOAD_FACTOR = 0.75f;

    private Entry<K, V>[] table;
    private int size;
    private int capacity;
    private float loadFactor;

    public MyHashMap() {
        this(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR);
    }

    public MyHashMap(int capacity, float loadFactor) {
        this.capacity = capacity;
        this.loadFactor = loadFactor;
        this.table = new Entry[capacity];
    }

    public void put(K key, V value) {
        int index = hash(key);
        Entry<K, V> entry = table[index];
        while (entry != null) {
            if (entry.key.equals(key)) {
                entry.value = value;
                return;
            }
            entry = entry.next;
        }
        Entry<K, V> newEntry = new Entry<>(key, value);
        newEntry.next = table[index];
        table[index] = newEntry;
        size++;
        if (size > capacity * loadFactor) {
            resize();
        }
    }

    public V get(K key) {
        int index = hash(key);
        Entry<K, V> entry = table[index];
        while (entry != null) {
            if (entry.key.equals(key)) {
                return entry.value;
            }
            entry = entry.next;
        }
        return null;
    }

    private int hash(K key) {
        return key.hashCode() % capacity;
    }

    private void resize() {
        capacity *= 2;
        Entry<K, V>[] newTable = new Entry[capacity];
        for (Entry<K, V> entry : table) {
            while (entry != null) {
                Entry<K, V> next = entry.next;
                int index = hash(entry.key);
                entry.next = newTable[index];
                newTable[index] = entry;
                entry = next;
            }
        }
        table = newTable;
    }

    private static class Entry<K, V> {
        K key;
        V value;
        Entry<K, V> next;

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