java a*算法 请写注释

好的，下面是 Java 实现 A* 算法的代码注释：

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.PriorityQueue;

public class AStar {

    //定义一个Node类表示每一个节点
    private static class Node implements Comparable<Node> {
        int x, y; //节点的坐标
        int g; //从起点到当前节点的实际距离
        int h; //从当前节点到终点的预计距离
        Node parent; //当前节点的父节点

        public Node(int x, int y) {
            this.x = x;
            this.y = y;
        }

        //计算当前节点的 f 值
        public int getF() {
            return g + h;
        }

        //比较两个节点的 f 值
        @Override
        public int compareTo(Node other) {
            return Integer.compare(this.getF(), other.getF());
        }

        //判断两个节点是否相同
        @Override
        public boolean equals(Object obj) {
            if (obj instanceof Node) {
                Node other = (Node)obj;
                return this.x == other.x && this.y == other.y;
            }
            return false;
        }

        //计算当前节点到终点的预计距离
        public void calcH(Node end) {
            this.h = Math.abs(end.x - this.x) + Math.abs(end.y - this.y);
        }
    }

    //定义地图的宽度和高度
    private static final int WIDTH = 10;
    private static final int HEIGHT = 10;

    //定义地图中的障碍物
    private static final int[][] MAP = new int[][]{
            {0, 0, 0, 0, 0, 0, 0, 0, 0, 0},
            {0, 1, 0, 0, 0, 0, 0, 0, 0, 0},
            {0, 1, 0, 0, 0, 0, 0, 0, 0, 0},
            {0, 1, 0, 0, 0, 0, 0, 0, 0, 0},
            {0, 1, 0, 0, 0, 0, 0, 0, 0, 0},
            {0, 1, 0, 0, 0, 0, 0, 0, 0, 0},
            {0, 1, 0, 0, 0, 0, 0, 0, 0, 0},
            {0, 1, 0, 0, 0, 0, 0, 0, 0, 0},
            {0, 1, 0, 0, 0, 0, 0, 0, 0, 0},
            {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
    };

    //判断一个节点是否在地图内
    private static boolean isValid(int x, int y) {
        return x >= 0 && x < WIDTH && y >= 0 && y < HEIGHT;
    }

    //判断一个节点是否为障碍物
    private static boolean isObstacle(int x, int y) {
        return MAP[y][x] == 1;
    }

    //查找周围可通过的节点
    private static ArrayList<Node> getNeighbors(Node node) {
        ArrayList<Node> neighbors = new ArrayList<>();
        int x = node.x;
        int y = node.y;
        int[][] directions = new int[][]{{-1, 0}, {0, -1}, {1, 0}, {0, 1}}; //四个方向
        for (int[] direction : directions) {
            int dx = direction[0];
            int dy = direction[1];
            int nx = x + dx;
            int ny = y + dy;
            if (isValid(nx, ny) && !isObstacle(nx, ny)) {
                neighbors.add(new Node(nx, ny));
            }
        }
        return neighbors;
    }

    //计算从起点到终点的最短路径
    private static ArrayList<Node> findPath(Node start, Node end) {
        PriorityQueue<Node> openList = new PriorityQueue<>(); //开放列表
        HashSet<Node> closeList = new HashSet<>(); //关闭列表

        start.g = 0;
        start.calcH(end);
        openList.add(start);

        while (!openList.isEmpty()) {
            Node current = openList.poll(); //取出 f 值最小的节点
            if (current.equals(end)) { //找到了终点
                ArrayList<Node> path = new ArrayList<>();
                while (current != null) {
                    path.add(current);
                    current = current.parent;
                }
                Collections.reverse(path); //反转路径
                return path;
            }
            closeList.add(current); //将当前节点加入关闭列表
            for (Node neighbor : getNeighbors(current)) { //遍历邻居节点
                if (closeList.contains(neighbor)) { //如果邻居节点已在关闭列表中，则跳过
                    continue;
                }
                int tentativeG = current.g + 1; //计算从起点到邻居节点的实际距离
                if (!openList.contains(neighbor) || tentativeG < neighbor.g) { //如果邻居节点不在开放列表中，或者当前路径更短
                    neighbor.g = tentativeG;
                    neighbor.calcH(end);
                    neighbor.parent = current; //更新邻居节点的父节点
                    if (!openList.contains(neighbor)) { //如果邻居节点不在开放列表中，则加入开放列表
                        openList.add(neighbor);
                    }
                }
            }
        }

        return null; //找不到路径
    }

    //测试
    public static void main(String[] args) {
        Node start = new Node(0, 0);
        Node end = new Node(9, 9);
        ArrayList<Node> path = findPath(start, end);
        if (path != null) {
            for (Node node : path) {
                System.out.println(node.x + "," + node.y);
            }
        } else {
            System.out.println("No path found");
        }
    }
}

希望这份注释能够帮助你理解 A* 算法的实现过程。