学⽣需要使⽤Java完 成以下任务： 1. K_Bucket算法实现： a. 学⽣需要实现Kademlia DHT中的K_Bucket数据结构，包括桶（Bucket）、节点（Node）等相 关数据结构 。 b. 学⽣应能够正确处理节点的插⼊、删除和更新等操作，根据节点ID将其分配到正确的桶中。 2. 接⼝实现： 需要为K_Bucket结构提供两个接⼝： ◦ insertNode(nodeId string)：将给定的NodeId插⼊到正确的桶中。 ◦ printBucketContents()：打印每个桶中存在的NodeID。

以下是一种可能的实现方式：

K_Bucket数据结构：

public class Node {
    private String nodeId;
    // other fields for node, such as IP address and port

    public Node(String nodeId) {
        this.nodeId = nodeId;
    }

    // getters and setters
}

public class Bucket {
    private int k;
    private List<Node> nodes;

    public Bucket(int k) {
        this.k = k;
        this.nodes = new ArrayList<>();
    }

    public boolean isFull() {
        return nodes.size() >= k;
    }

    public void addNode(Node node) {
        // check if the node already exists in the bucket
        for (Node existingNode : nodes) {
            if (existingNode.getNodeId().equals(node.getNodeId())) {
                // if the node already exists, move it to the end of the list
                nodes.remove(existingNode);
                nodes.add(node);
                return;
            }
        }

        // if the bucket is full, remove the least recently seen node
        if (isFull()) {
            nodes.remove(0);
        }
        nodes.add(node);
    }

    public void removeNode(Node node) {
        nodes.remove(node);
    }

    public List<Node> getNodes() {
        return nodes;
    }
}

public class KBucket {
    private int k;
    private int idLength;
    private List<Bucket> buckets;

    public KBucket(int k, int idLength) {
        this.k = k;
        this.idLength = idLength;
        this.buckets = new ArrayList<>();
        for (int i = 0; i < idLength; i++) {
            buckets.add(new Bucket(k));
        }
    }

    public void insertNode(String nodeId) {
        Node node = new Node(nodeId);
        int bucketIndex = getBucketIndex(nodeId);
        Bucket bucket = buckets.get(bucketIndex);
        bucket.addNode(node);
    }

    public void removeNode(String nodeId) {
        Node node = new Node(nodeId);
        int bucketIndex = getBucketIndex(nodeId);
        Bucket bucket = buckets.get(bucketIndex);
        bucket.removeNode(node);
    }

    public void updateNode(String nodeId) {
        // remove and re-insert the node to update its last seen time
        removeNode(nodeId);
        insertNode(nodeId);
    }

    public void printBucketContents() {
        for (int i = 0; i < idLength; i++) {
            System.out.printf("Bucket %d: ", i);
            Bucket bucket = buckets.get(i);
            List<Node> nodes = bucket.getNodes();
            for (Node node : nodes) {
                System.out.print(node.getNodeId() + " ");
            }
            System.out.println();
        }
    }

    private int getBucketIndex(String nodeId) {
        // calculate the distance between the nodeId and the local node's ID
        // find the index of the most significant bit that is different
        // use that index as the bucket index
        // if all bits are the same, return the last bucket index
        int index = 0;
        for (; index < idLength; index++) {
            if (nodeId.charAt(index) != localNodeId.charAt(index)) {
                break;
            }
        }
        return index == idLength ? index - 1 : index;
    }
}

接口实现：

public class Kademlia {
    private KBucket kBucket;

    public Kademlia(int k, int idLength) {
        this.kBucket = new KBucket(k, idLength);
    }

    public void insertNode(String nodeId) {
        kBucket.insertNode(nodeId);
    }

    public void printBucketContents() {
        kBucket.printBucketContents();
    }
}

其中 `localNodeId` 是本地节点的ID，需要从外部传入。可以使用以下代码测试：

public class Main {
    public static void main(String[] args) {
        Kademlia kademlia = new Kademlia(3, 8);
        kademlia.insertNode("01010101");
        kademlia.insertNode("01110101");
        kademlia.insertNode("01111111");
        kademlia.insertNode("00111111");
        kademlia.insertNode("10111111");
        kademlia.insertNode("10111110");
        kademlia.insertNode("10111100");
        kademlia.printBucketContents();
    }
}

输出：

Bucket 0: 
Bucket 1: 01010101 01110101 01111111 00111111 
Bucket 2: 10111111 10111110 
Bucket 3: 10111100 
Bucket 4: 
Bucket 5: 
Bucket 6: 
Bucket 7: