Implement Hashmap in Java. 

原理： Hashmap就是array of linkedlist，就是利用hash算法，算index之后，然后冲突了，就看后面有没有 Key Value pair 相等，如果相同，则覆盖，如果没有，则加在bucket的beginning。 源代码： http://developer.classpath.org/doc/java/util/HashMap-source.html

public class ImplementHashMap {
	 class Node{
		 String key;
		 Integer val;
		 Node next;
		 public Node(String key, Integer val){
			 this.key = key;
			 this.val = val;
		 }
	 }
	
	 private int size = 3;
	 private Node[] array;
	public ImplementHashMap() {
		array = new Node[size];
	}
	
	public void put(String key, Integer value){
		int index = key.hashCode()%this.size;
		System.out.println("index is:"+index);
		Node node = array[index];
		while(node!=null) {
			if(node.key.equals(key)){
				node.val = value;
				return;
			} else {
				node = node.next;
			}
		}
		
		// add new entry to the beginning of the bucket;
		Node newnode = new Node(key,value);
		newnode.next = array[index];
		array[index] = newnode;
		return;
	}
	
	public Integer get(String key){
		int index = key.hashCode()%this.size;
		Node node = array[index];
		while(node!=null){
			if(node.key.equals(key)){
				return node.val;
			} else {
				node = node.next;
			}
		}
		return null;
	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ImplementHashMap hashmap = new ImplementHashMap();
		
		hashmap.put("a", 2);
		System.out.println(hashmap.get("a"));
		
		hashmap.put("b", 5);
		System.out.println(hashmap.get("b"));

		hashmap.put("c", 7);
		System.out.println(hashmap.get("c"));
		
		hashmap.put("d", 8);
		System.out.println(hashmap.get("d"));
		
		hashmap.put("e", 9);
		System.out.println(hashmap.get("e"));
		
		hashmap.put("f", 10);
		System.out.println(hashmap.get("f"));

	}

}

index is:1

2

index is:2

5

index is:0

7

index is:1

8

index is:2

9

index is:0

10