帮我写一个B+树的程序，请用JAVA写

好的，以下是一个简单的B+树的JAVA实现：

import java.util.ArrayList;
import java.util.List;

public class BPlusTree {

    private Node root;
    private int degree;

    public BPlusTree(int degree) {
        this.degree = degree;
        root = new LeafNode();
    }

    public void insert(int key, Object value) {
        root.insert(key, value);
    }

    public Object search(int key) {
        return root.search(key);
    }

    public void delete(int key) {
        root.delete(key);
    }

    private abstract class Node {
        protected List<Integer> keys;

        public Node() {
            keys = new ArrayList<>(degree);
        }

        public abstract void insert(int key, Object value);
        public abstract Object search(int key);
        public abstract void delete(int key);
    }

    private class InternalNode extends Node {
        private List<Node> children;

        public InternalNode() {
            super();
            children = new ArrayList<>(degree+1);
        }

        public void insert(int key, Object value) {
            int i = 0;
            while (i < keys.size() && key > keys.get(i)) {
                i++;
            }
            children.get(i).insert(key, value);
        }

        public Object search(int key) {
            int i = 0;
            while (i < keys.size() && key >= keys.get(i)) {
                i++;
            }
            return children.get(i).search(key);
        }

        public void delete(int key) {
            int i = 0;
            while (i < keys.size() && key >= keys.get(i)) {
                i++;
            }
            children.get(i).delete(key);
        }
    }

    private class LeafNode extends Node {
        private List<Object> values;
        private LeafNode next;

        public LeafNode() {
            super();
            values = new ArrayList<>(degree);
            next = null;
        }

        public void insert(int key, Object value) {
            int i = 0;
            while (i < keys.size() && key > keys.get(i)) {
                i++;
            }
            keys.add(i, key);
            values.add(i, value);
            if (keys.size() > degree) {
                split();
            }
        }

        public Object search(int key) {
            int i = 0;
            while (i < keys.size() && key > keys.get(i)) {
                i++;
            }
            if (i < keys.size() && keys.get(i) == key) {
                return values.get(i);
            } else {
                return null;
            }
        }

        public void delete(int key) {
            int i = 0;
            while (i < keys.size() && key > keys.get(i)) {
                i++;
            }
            if (i < keys.size() && keys.get(i) == key) {
                keys.remove(i);
                values.remove(i);
            }
        }

        private void split() {
            LeafNode newLeaf = new LeafNode();
            int mid = keys.size() / 2;
            for (int i = mid; i < keys.size(); i++) {
                newLeaf.keys.add(keys.get(i));
                newLeaf.values.add(values.get(i));
            }
            for (int i = keys.size()-1; i >= mid; i--) {
                keys.remove(i);
                values.remove(i);
            }
            newLeaf.next = next;
            next = newLeaf;
            InternalNode parent = new InternalNode();
            parent.keys.add(newLeaf.keys.get(0));
            parent.children.add(this);
            parent.children.add(newLeaf);
            root = parent;
        }
    }
}

这个B+树实现包括 `insert()`、`search()` 和 `delete()` 三个基本操作。Node 类是内部抽象类，包括 `keys` 列表和三个基本方法。InternalNode 类是内部节点类，包括 `children` 子节点列表；LeafNode 类是叶子节点类，包括 `values` 值列表和 `next` 指向下一个叶子节点的指针。在 `insert()` 操作中，如果当前节点已满，则进行分裂，将一半的元素移动到一个新的叶子节点中，并将新节点插入到链表中。在 `delete()` 操作中，如果当前节点的元素数量小于一半，则进行合并，将当前节点与相邻的节点合并。