java - 当每个实例传递唯一值时，自定义 "Node"类的两个实例都会打印相同的值

Question

我正在尝试基于 Entry 对象创建一个新节点。我检索 2 个不同的条目并打印出它们的键和值。打印出来的两个 key 是不同的。我将每个键和值存储到单独的“节点”n1 和 n2 中。 Node 是我创建的自定义类，其代码可以在下面找到。当我打印出 n1 的键和 n2 的键的值时，它们应该是不同的，因为条目的键是，但由于某种原因它打印出相同的值。我不知道为什么会发生这种情况，我也想不通。这是我目前的代码:

节点类:

import java.util.HashMap;
import java.util.Map.Entry;

public class Node {
    public static Entry<String, Integer> keyVal;
    public static Node leftChild;
    public static Node rightChild;
    public static String bitCode;

    public Node() {
        keyVal = null;
        leftChild = null;
        rightChild = null;
    }

    public Node(Entry<String, Integer> entry) {
        keyVal = entry;
        leftChild = null;
        rightChild = null;
    }

    public Node(Entry<String, Integer> entry, Node n1, Node n2) {
        keyVal = entry;
        leftChild = n1;
        rightChild = n2;
    }

    public Entry<String, Integer> getEntry() { return keyVal; }

    public Node getLeftChild() { return leftChild; }

    public Node getRightChild() { return rightChild; }

    public void setLeftChild(Node lc) {
        leftChild = lc;
    }

    public void setRightChild(Node rc) {
        leftChild = rc;
    }
}

主类中的createTree方法:

private static Node createTree(PriorityQueue<Entry<String, Integer>> pq) {
    map = new HashMap<>();    // Defined as a public attribute to the Main class
    Entry<String, Integer> entry1 = null;
    Entry<String, Integer> entry2 = null;
    Entry<String, Integer> parent = null;
    Node n1 = null;
    Node n2 = null;
    Node n3 = null;
    System.out.println("PQ size: " + pq.size());

    while (pq.size() > 1) {
        entry1 = pq.poll();
        // Prints "Entry1: R 1"
        System.out.println("Entry1: " + entry1.getKey() + " " + entry1.getValue());    

        entry2 = pq.poll();
        // Prints "Entry2: e 1"
        System.out.println("Entry2: " + entry2.getKey() + " " + entry2.getValue());

        // Never enters if, goes to else
        if (map.containsKey(entry1.getKey())) {
            System.out.println("Map contains entry1!");
            n1 = map.get(entry1.getKey());
        } else {
            n1 = new Node(entry1);              
        }
        // Never enters if, goes to else
        if (map.containsKey(entry2.getKey())) {
            System.out.println("Map contains entry2!");    
            n2 = map.get(entry2.getKey());
        } else {
            n2 = new Node(entry2);              
        }
        // Should print "N1: R 1", Instead prints "N1: e 1"
        System.out.println("N1: " + n1.getEntry().getKey() + " " + n1.getEntry().getValue());
        // Prints "N2: R 1"
        System.out.println("N2: " + n2.getEntry().getKey() + " " + n2.getEntry().getValue());
    }

Answer 1

发生这种情况是因为类 Node 中的成员是静态的:

//From the 'Node' class:
public static Entry<String, Integer> keyVal;
public static Node leftChild;
public static Node rightChild;
public static String bitCode;
//...

因此，当您创建第二个 Node 时，执行以下操作:

 n1 = new Node(entry1);

您覆盖首先输入的值:

n2 = new Node(entry2);