簡單實現HashMap 原理

簡單實現HashMap中數組 + 鏈表

1. 新建數組，
2. 添加的元素下標   爲    hashCode % 數組長度 
3. 裏面存儲自定義節點對象，下標值相同的存儲到next中，依次向下存儲

public class MyHashMap<K, V> {
    //節點數組
    private Entry<K, V>[] table;
    //定義初始數組容量
    private static Integer CAPACITRY = 5;
    //元素數量
    private Integer size = 0;

    //封裝一個節點
    class Entry<K, V> {
        private K k;
        private V v;
        private Entry<K, V> next;

        public Entry(K k, V v, Entry<K, V> next) {
            this.k = k;
            this.v = v;
            this.next = next;
        }

        @Override
        public String toString() {
            return this.k+"-"+this.v+"-"+ this.next;
        }
    }

    public MyHashMap() {
        //自定義一個數組進行存放元素
        this.table = new Entry[CAPACITRY];
    }

    public int size() {
        return size;
    }

    public V get(K key) {
        Integer hash = key.hashCode();
        Integer index = hash % table.length;
        for (Entry<K, V> entry = table[index]; entry != null; entry = entry.next) {
            if (key.equals(entry.k)) {
                return entry.v;
            }
        }
        return null;

    }


    public Object put(K key, V value) {

        Integer hash = key.hashCode();
        System.out.println("hash=="+hash);
        //下標  哈希值 對 數組長度 取模
        //下標值爲 0 - 數組長度的值 這樣能分配數組
        Integer index = hash % table.length;
        //覆蓋舊Value
        for (Entry<K, V> entry = table[index]; entry != null; entry = entry.next) {

            if (key.equals(entry.k)) {
                //V oldValue = entry.v;
                entry.v = value;
                //return oldValue;
            }
        }
        //存儲節點對象  節點對象中存儲着key和value 並且含有指針指向head
        addEntry(key, value, index);
        return null;
    }

    private void addEntry(K key, V value, Integer index) {
        System.out.println(table[index]);
        table[index] = new Entry<>(key, value, table[index]);
        size++;
    }

    public static <V, K> void main(String[] args) {
        MyHashMap myHashMap = new MyHashMap();
        myHashMap.put(1,"張三1");
        myHashMap.put(2,"張三2");
        myHashMap.put(3,"張三3");
        myHashMap.put(4,"張三4");
        myHashMap.put(5,"張三5");
        myHashMap.put(6,"張三6");

    }
}