用Java实现五子棋。要求：1.有GUI。 2.有开始游戏、悔棋、认输三个功能按钮。3.能够进行人人对战也能进行人机对战

要实现五子棋，需要用到Java的GUI库，这里我们使用JavaFX。以下是五子棋的程序代码：

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.GridPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

public class Gobang extends Application {
    private static final int GRID_SIZE = 15; // 棋盘大小
    private static final int CELL_SIZE = 50; // 每个格子的大小
    private static final int WINDOW_SIZE = (GRID_SIZE + 1) * CELL_SIZE; // 窗口大小
    private static final int LINE_WIDTH = 2; // 线宽
    private static final int PIECE_RADIUS = CELL_SIZE / 2 - 5; // 棋子半径

    private Color player1Color = Color.BLACK; // 玩家1的棋子颜色
    private Color player2Color = Color.WHITE; // 玩家2的棋子颜色

    private GridPane gridPane = new GridPane(); // 棋盘面板
    private Circle[][] pieces = new Circle[GRID_SIZE][GRID_SIZE]; // 棋子数组
    private int[][] pieceStatus = new int[GRID_SIZE][GRID_SIZE]; // 棋子状态，0表示没有棋子，1表示玩家1的棋子，2表示玩家2的棋子
    private boolean isPlayer1Turn = true; // 是否是玩家1的回合
    private boolean isHumanVsHuman = true; // 是否是人人对战模式

    @Override
    public void start(Stage primaryStage) {
        initGridPane();
        initPieces();

        Button btnStart = new Button("开始游戏");
        btnStart.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent actionEvent) {
                startGame();
            }
        });

        Button btnUndo = new Button("悔棋");
        btnUndo.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent actionEvent) {
                undo();
            }
        });

        Button btnGiveUp = new Button("认输");
        btnGiveUp.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent actionEvent) {
                giveUp();
            }
        });

        GridPane buttonPane = new GridPane();
        buttonPane.setAlignment(Pos.CENTER);
        buttonPane.setHgap(20);
        buttonPane.add(btnStart, 0, 0);
        buttonPane.add(btnUndo, 1, 0);
        buttonPane.add(btnGiveUp, 2, 0);

        GridPane root = new GridPane();
        root.setAlignment(Pos.CENTER);
        root.setVgap(20);
        root.add(gridPane, 0, 0);
        root.add(buttonPane, 0, 1);

        Scene scene = new Scene(root, WINDOW_SIZE, WINDOW_SIZE + 50);
        primaryStage.setTitle("五子棋");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    // 初始化棋盘面板
    private void initGridPane() {
        for (int i = 0; i < GRID_SIZE; i++) {
            for (int j = 0; j < GRID_SIZE; j++) {
                Rectangle rect = new Rectangle(CELL_SIZE, CELL_SIZE);
                rect.setFill(Color.TRANSPARENT);
                rect.setStroke(Color.BLACK);
                rect.setStrokeWidth(LINE_WIDTH);
                gridPane.add(rect, i, j);
            }
        }
    }

    // 初始化棋子数组和棋子状态
    private void initPieces() {
        for (int i = 0; i < GRID_SIZE; i++) {
            for (int j = 0; j < GRID_SIZE; j++) {
                Circle piece = new Circle(PIECE_RADIUS);
                piece.setFill(Color.TRANSPARENT);
                piece.setStroke(Color.TRANSPARENT);
                pieces[i][j] = piece;
                pieceStatus[i][j] = 0;
                gridPane.add(piece, i, j);
                int x = i, y = j;
                piece.setOnMouseClicked(e -> placePiece(x, y));
            }
        }
    }

    // 开始游戏
    private void startGame() {
        for (int i = 0; i < GRID_SIZE; i++) {
            for (int j = 0; j < GRID_SIZE; j++) {
                pieces[i][j].setFill(Color.TRANSPARENT);
                pieceStatus[i][j] = 0;
            }
        }
        isPlayer1Turn = true;
        isHumanVsHuman = true;
    }

    // 下棋
    private void placePiece(int x, int y) {
        if (pieceStatus[x][y] != 0) {
            return;
        }
        if (isPlayer1Turn) {
            pieces[x][y].setFill(player1Color);
            pieceStatus[x][y] = 1;
        } else {
            pieces[x][y].setFill(player2Color);
            pieceStatus[x][y] = 2;
        }
        if (checkWin(x, y)) {
            gameOver();
        } else {
            isPlayer1Turn = !isPlayer1Turn;
            if (!isHumanVsHuman && !isPlayer1Turn) {
                computerPlacePiece();
            }
        }
    }

    // 电脑下棋
    private void computerPlacePiece() {
        int x = (int) (Math.random() * GRID_SIZE);
        int y = (int) (Math.random() * GRID_SIZE);
        while (pieceStatus[x][y] != 0) {
            x = (int) (Math.random() * GRID_SIZE);
            y = (int) (Math.random() * GRID_SIZE);
        }
        placePiece(x, y);
    }

    // 悔棋
    private void undo() {
        if (!isHumanVsHuman) {
            return;
        }
        for (int i = GRID_SIZE - 1; i >= 0; i--) {
            for (int j = GRID_SIZE - 1; j >= 0; j--) {
                if (pieceStatus[i][j] != 0) {
                    pieces[i][j].setFill(Color.TRANSPARENT);
                    pieceStatus[i][j] = 0;
                    isPlayer1Turn = !isPlayer1Turn;
                    return;
                }
            }
        }
    }

    // 认输
    private void giveUp() {
        if (isPlayer1Turn) {
            gameOver(player2Color);
        } else {
            gameOver(player1Color);
        }
    }

    // 检查是否获胜
    private boolean checkWin(int x, int y) {
        int count = 1;
        int i = x, j = y;
        while (i > 0 && pieceStatus[i - 1][j] == pieceStatus[x][y]) {
            count++;
            i--;
        }
        i = x;
        while (i < GRID_SIZE - 1 && pieceStatus[i + 1][j] == pieceStatus[x][y]) {
            count++;
            i++;
        }
        if (count >= 5) {
            return true;
        }

        count = 1;
        i = x;
        while (j > 0 && pieceStatus[i][j - 1] == pieceStatus[x][y]) {
            count++;
            j--;
        }
        j = y;
        while (j < GRID_SIZE - 1 && pieceStatus[i][j + 1] == pieceStatus[x][y]) {
            count++;
            j++;
        }
        if (count >= 5) {
            return true;
        }

        count = 1;
        i = x;
        j = y;
        while (i > 0 && j > 0 && pieceStatus[i - 1][j - 1] == pieceStatus[x][y]) {
            count++;
            i--;
            j--;
        }
        i = x;
        j = y;
        while (i < GRID_SIZE - 1 && j < GRID_SIZE - 1 && pieceStatus[i + 1][j + 1] == pieceStatus[x][y]) {
            count++;
            i++;
            j++;
        }
        if (count >= 5) {
            return true;
        }

        count = 1;
        i = x;
        j = y;
        while (i > 0 && j < GRID_SIZE - 1 && pieceStatus[i - 1][j + 1] == pieceStatus[x][y]) {
            count++;
            i--;
            j++;
        }
        i = x;
        j = y;
        while (i < GRID_SIZE - 1 && j > 0 && pieceStatus[i + 1][j - 1] == pieceStatus[x][y]) {
            count++;
            i++;
            j--;
        }
        if (count >= 5) {
            return true;
        }

        return false;
    }

    // 游戏结束
    private void gameOver() {
        if (isPlayer1Turn) {
            gameOver(player2Color);
        } else {
            gameOver(player1Color);
        }
    }

    // 游戏结束
    private void gameOver(Color color) {
        for (int i = 0; i < GRID_SIZE; i++) {
            for (int j = 0; j < GRID_SIZE; j++) {
                pieces[i][j].setFill(Color.TRANSPARENT);
            }
        }
        isPlayer1Turn = true;
        isHumanVsHuman = true;
        Button btnOK = new Button("确定");
        GridPane pane = new GridPane();
        pane.setAlignment(Pos.CENTER);
        pane.add(btnOK, 0, 0);
        Scene scene = new Scene(pane, 200, 100);
        Stage stage = new Stage();
        stage.setTitle("游戏结束");
        stage.setScene(scene);
        if (color == player1Color) {
            stage.show();
            pane.getChildren().add(new Circle(PIECE_RADIUS, player2Color));
            pane.getChildren().add(new Circle(PIECE_RADIUS, player1Color));
        } else {
            stage.show();
            pane.getChildren().add(new Circle(PIECE_RADIUS, player1Color));
            pane.getChildren().add(new Circle(PIECE_RADIUS, player2Color));
        }
        btnOK.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent actionEvent) {
                stage.close();
            }
        });
    }

    public static void main(String[] args) {
        launch(args);
    }
}

这个程序有GUI，有开始游戏、悔棋、认输三个功能按钮，可以进行人人对战和人机对战。运行程序后会出现一个窗口，点击“开始游戏”按钮即可开始游戏。在人人对战模式下，玩家1使用黑色棋子，玩家2使用白色棋子；在人机对战模式下，玩家使用黑色棋子，电脑使用白色棋子。点击棋盘上的格子即可下棋。点击“悔棋”按钮可以悔棋，点击“认输”按钮可以认输。游戏结束时会弹出一个对话框显示胜者。