HashMap实现原理简析及实现的demo（一看就明白）

 1   transient Node<K,V>[] table;
 2  static class Node<K,V> implements Map.Entry<K,V> {
 3         final int hash;
 4         final K key;
 5         V value;
 6         Node<K,V> next;
 7 
 8         Node(int hash, K key, V value, Node<K,V> next) {
 9             this.hash = hash;
10             this.key = key;
11             this.value = value;
12             this.next = next;
13         }
14 //.....
15 }

 1 public class HashMapDemo<K, V> {
 2 
 3     private class Entry<K, V> {
 4         int hash;
 5         K key;
 6         V value;
 7         Entry<K, V> next;
 8  
 9         Entry(int hash, K key, V value, Entry<K, V> next) {
10             this.hash = hash;
11             this.key = key;
12             this.value = value;
13             this.next = next;
14         }
15     }
16  
17     private static final int DEFAULT_CAPACITY = 1 << 4;
18  
19     private Entry<K, V>[] table;
20  
21     private int capacity;
22  
23     private int size;
24  
25     public HashMapDemo() {
26         this(DEFAULT_CAPACITY);
27     }
28  
29     public HashMapDemo(int capacity) {
30         if (capacity < 0) {
31             throw new IllegalArgumentException();
32         } else {
33             table = new Entry[capacity];
34             size = 0;
35             this.capacity = capacity;
36         }
37     }
38  
39     public int size() {
40         return size;
41     }
42  
43     public boolean isEmpty() {
44         return size == 0 ? true : false;
45     }
46  
47     private int hash(K key) {
48         double tmp = key.hashCode() * (Math.pow(5, 0.5) - 1) / 2;
49         double digit = tmp - Math.floor(tmp);
50         return (int) Math.floor(digit * capacity);
51     }
52  
53     public void put(K key, V value) {
54         if (key == null) {
55             throw new IllegalArgumentException();
56         }
57         int hash = hash(key);
58         Entry<K, V> nEntry = new Entry<K, V>(hash, key, value, null);
59         Entry<K, V> entry = table[hash];
60         while (entry != null) {
61             if (entry.key.equals(key)) {
62                 entry.value = value;
63                 return;
64             }
65             entry = entry.next;
66         }
67         nEntry.next = table[hash];
68         table[hash] = nEntry;
69         size++;
70     }
71  
72     public V get(K key) {
73         if (key == null) {
74             throw new IllegalArgumentException();
75         }
76         int hash = hash(key);
77         Entry<K, V> entry = table[hash];
78         while (entry != null) {
79             if (entry.key.equals(key)) {
80                 return entry.value;
81             }
82             entry = entry.next;
83         }
84         return null;
85     }
86  
87     public static void main(String[] args) {
88         HashMapDemo<String, String> map = new HashMapDemo<String, String>();
89         map.put("1", "11");
90         map.put("1", "22");
91         map.put("3", "33");
92         System.out.println(map.get("1"));
93         System.out.println(map.get("3"));
94     }
95 
96 }