你真的了解Java的HashMap吗？

import java.util.ArrayList;
import java.util.List;
//Node对象
public class Node {
	public int val;
	public List neighbors;

	public Node() {
		val = 0;
		neighbors = new ArrayList();
	}

	public Node(int _val) {
		val = _val;
		neighbors = new ArrayList();
	}

	public Node(int _val, ArrayList _neighbors) {
		val = _val;
		neighbors = _neighbors;
	}
}

public class test {
	private static Map map = new HashMap<>();
	public static void main(String[] args) {
		Node node = new Node();//创建一个Node对象
		map.put(1, node);//把它放进我们的哈希表中
		node.val = 100;//然后赋值给我们new 出来的node对象
		System.out.println(node);
		System.out.println(map.get(1));
		System.out.println(node == map.get(1));
		System.out.println(map.get(1).val);
	}
}