请用Java编写一个简易五子棋程序

好的，以下是一个简易五子棋程序的Java代码：

import java.util.Scanner;

public class Gobang {
    public static final int BOARD_SIZE = 15;
    public static String[][] board = new String[BOARD_SIZE][BOARD_SIZE];

    public static void main(String[] args) {
        initializeBoard();
        printBoard();
        Scanner scanner = new Scanner(System.in);
        int x, y;
        String winner = null;
        boolean isBlack = true;
        while (winner == null) {
            System.out.print("请输入落子的坐标（x,y）：");
            x = scanner.nextInt();
            y = scanner.nextInt();
            if (x < 0 || x >= BOARD_SIZE || y < 0 || y >= BOARD_SIZE) {
                System.out.println("坐标不合法，请重新输入！");
                continue;
            }
            if (board[x][y] != null) {
                System.out.println("该位置已经有棋子，请重新输入！");
                continue;
            }
            board[x][y] = isBlack ? "●" : "○";
            printBoard();
            isBlack = !isBlack;
            winner = checkWinner(x, y);
        }
        System.out.println("胜者是：" + winner);
    }

    public static void initializeBoard() {
        for (int i = 0; i < BOARD_SIZE; i++) {
            for (int j = 0; j < BOARD_SIZE; j++) {
                board[i][j] = "+";
            }
        }
    }

    public static void printBoard() {
        System.out.print("  ");
        for (int i = 0; i < BOARD_SIZE; i++) {
            System.out.print((char) ('a' + i) + " ");
        }
        System.out.println();
        for (int i = 0; i < BOARD_SIZE; i++) {
            System.out.print((i + 1) + " ");
            for (int j = 0; j < BOARD_SIZE; j++) {
                System.out.print(board[i][j] + " ");
            }
            System.out.println((i + 1));
        }
        System.out.print("  ");
        for (int i = 0; i < BOARD_SIZE; i++) {
            System.out.print((char) ('a' + i) + " ");
        }
        System.out.println();
    }

    public static String checkWinner(int x, int y) {
        String target = board[x][y];
        int count = 1;
        for (int i = x + 1; i < BOARD_SIZE && board[i][y] == target; i++) {
            count++;
        }
        for (int i = x - 1; i >= 0 && board[i][y] == target; i--) {
            count++;
        }
        if (count >= 5) {
            return target;
        }

        count = 1;
        for (int j = y + 1; j < BOARD_SIZE && board[x][j] == target; j++) {
            count++;
        }
        for (int j = y - 1; j >= 0 && board[x][j] == target; j--) {
            count++;
        }
        if (count >= 5) {
            return target;
        }

        count = 1;
        for (int i = x + 1, j = y + 1; i < BOARD_SIZE && j < BOARD_SIZE && board[i][j] == target; i++, j++) {
            count++;
        }
        for (int i = x - 1, j = y - 1; i >= 0 && j >= 0 && board[i][j] == target; i--, j--) {
            count++;
        }
        if (count >= 5) {
            return target;
        }

        count = 1;
        for (int i = x + 1, j = y - 1; i < BOARD_SIZE && j >= 0 && board[i][j] == target; i++, j--) {
            count++;
        }
        for (int i = x - 1, j = y + 1; i >= 0 && j < BOARD_SIZE && board[i][j] == target; i--, j++) {
            count++;
        }
        if (count >= 5) {
            return target;
        }

        return null;
    }
}

该程序使用二维数组来表示棋盘，使用字符串 "●" 和 "○" 分别表示黑子和白子。程序先初始化棋盘，然后循环让玩家输入落子的坐标，检查坐标的合法性和该位置是否已经有棋子，然后更新棋盘、打印棋盘、切换玩家，并且在每次落子后检查是否有胜者出现。如果出现胜者，程序退出循环并且输出胜者的颜色。