我正在尝试使用Arraylist实现撤消移动功能。我创建了一个Arraylist，它包含Move对象，在每次有效移动（'U'，'D'，'L'，'R'）时，它会在Arraylist中添加一个新的移动对象。这是正常的，在这个阶段，我正在尝试从Arraylist中删除最后一个对象，每次按下'Z'但它只进行一次删除，任何其他后续按'Z'不会改变任何东西。
任何人都可以查看下面的代码，让我知道我做错了什么？
实现/问题在move方法中，这是switch语句中的最后一种情况。
package secondproject;
import java.util.ArrayList;
import java.util.Random;
import java.util.Scanner;
public class Game {
private static final int BOARD_SIZE = 10;
private static final int INITIAL_PLAYER_COL = 0;
private static final int INITIAL_PLAYER_ROW = BOARD_SIZE - 1;
private static final int HOME_COL = BOARD_SIZE - 1;
private static final int HOME_ROW = 0;
private static final int WALL_LENGTH = 5;
private static final char PLAYER_CHAR = 'P';
private static final char HOME_CHAR = 'H';
private static final char WALL_CHAR = 'X';
private static final char FREE_SQUARE_CHAR = '.';
private static final char DOUGHNUT_CHAR = '@';
private static final char UP_MOVE_CHAR = 'U';
private static final char DOWN_MOVE_CHAR = 'D';
private static final char LEFT_MOVE_CHAR = 'L';
private static final char RIGHT_MOVE_CHAR = 'R';
private static final char UNDO_MOVE_CHAR = 'Z';
private static final char TRAIL_CHAR = 'M';
private static char[][] board = new char[BOARD_SIZE][BOARD_SIZE];
private static Scanner scan = new Scanner(System.in);
private static Scanner keyBoard = new Scanner(System.in);
private static int playerCol = INITIAL_PLAYER_COL;
private static int playerRow = INITIAL_PLAYER_ROW;
private static int nbrDoughnuts = 0;
private static int nbrMoves = 0;
private static Random random = new Random();
private static int lives = 1;
private static int doughnutLives;
private static boolean doughnutCheck;
static ArrayList<Move> movement = new ArrayList<Move>();
public static void main(String[] args) {
setUpBoard();
showBoard();
String opt;
do {
System.out.print("Next option ?");
opt = scan.next();
char opt1 = opt.charAt(0);
if (opt1 == UP_MOVE_CHAR || opt1 == DOWN_MOVE_CHAR
|| opt1 == LEFT_MOVE_CHAR || opt1 == RIGHT_MOVE_CHAR
|| opt1 == UNDO_MOVE_CHAR) {
move(opt1);
//undoMove(opt1);
} else {
System.out.println("Allowed commands are: + " + UP_MOVE_CHAR
+ "," + DOWN_MOVE_CHAR + "," + LEFT_MOVE_CHAR
+ "," + RIGHT_MOVE_CHAR);
}
showBoard();
System.out.println("Number of moves made = " + nbrMoves);
System.out.println("Number of doughnuts eaten = " + nbrDoughnuts);
System.out.println("Lives = " + lives);
} while (board[HOME_ROW][HOME_COL] == HOME_CHAR);
System.out.println("Thank you and goodbye");
}
/**
* Set up the initial state of the board
*/
private static void setUpBoard() {
intialiseBoard(); // Fill the board with . characters
//Add the first vertical wall
int v1StartCol = 1 + random.nextInt(BOARD_SIZE - 2);
int v1StartRow = 1 + random.nextInt(BOARD_SIZE - WALL_LENGTH - 1);
addVerticalWall(v1StartCol, v1StartRow, WALL_LENGTH);
//Add the second vertical wall
int v2StartCol;
do {
v2StartCol = 1 + random.nextInt(BOARD_SIZE - 2);
} while (v2StartCol == v1StartCol);
int v2StartRow = 1 + random.nextInt(BOARD_SIZE - WALL_LENGTH - 1);
addVerticalWall(v2StartCol, v2StartRow, WALL_LENGTH);
//Add the horizontal wall
int h1StartRow = 1 + random.nextInt(BOARD_SIZE - 2);
int h1StartCol = 1 + random.nextInt(BOARD_SIZE - WALL_LENGTH - 1);
addHorizontalWall(h1StartCol, h1StartRow, WALL_LENGTH);
//Add the dougnuts
int nbrDoughnutsAdded = 0;
while (nbrDoughnutsAdded < 5) {
int dRow = 1 + random.nextInt(BOARD_SIZE - 2);
int dCol = 1 + random.nextInt(BOARD_SIZE - 2);
if (board[dRow][dCol] == FREE_SQUARE_CHAR) {
board[dRow][dCol] = DOUGHNUT_CHAR;
nbrDoughnutsAdded++;
}
}
//Add the player and the home square
board[playerRow][playerCol] = PLAYER_CHAR;
board[HOME_ROW][HOME_COL] = HOME_CHAR;
}
/**
* Add a vertical wall to the board
*
* @param startCol Column on which wall is situated
* @param startRow Row on which top of wall is situated
* @param length Number of squares occupied by wall
*/
private static void addVerticalWall(int startCol, int startRow, int length) {
for (int row = startRow; row < startRow + length; row++) {
board[row][startCol] = WALL_CHAR;
}
}
/**
* Add a horizontal wall to the board
*
* @param startCol Column on which leftmost end of wall is situated
* @param startRow Row on which wall is situated
* @param length Number of squares occupied by wall
*/
private static void addHorizontalWall(int startCol, int startRow, int length) {
for (int col = startCol; col < startCol + length; col++) {
board[startRow][col] = WALL_CHAR;
}
}
/**
* Display the board
*/
private static void showBoard() {
for (int row = 0; row < board.length; row++) {
for (int col = 0; col < board[row].length; col++) {
System.out.print(board[row][col]);
}
System.out.println();
}
}
/**
* Fill the board with FREE_SQUARE_CHAR characters.
*/
private static void intialiseBoard() {
for (int row = 0; row < board.length; row++) {
for (int col = 0; col < board[row].length; col++) {
board[row][col] = FREE_SQUARE_CHAR;
}
System.out.println();
}
}
/**
* Move the player
*
* @param moveChar Character indicating the move to be made
*/
private static void move(char moveChar) {
int newCol = playerCol;
int newRow = playerRow;
switch (moveChar) {
case UP_MOVE_CHAR:
if (lives == 1) {
newRow--;
} else if (lives > 1) {
int number = keyBoard.nextInt();
if (number <= lives) {
newRow = newRow - number;
} else {
checkLives();
}
}
break;
case DOWN_MOVE_CHAR:
if (lives == 1) {
newRow++;
} else if (lives > 1) {
squareNumberPrompt();
int number = keyBoard.nextInt();
if (number <= lives) {
newRow = newRow + number;
} else {
checkLives();
}
}
break;
case LEFT_MOVE_CHAR:
if (lives == 1) {
newCol--;
} else if (lives > 1) {
squareNumberPrompt();
int number = keyBoard.nextInt();
if (number <= lives) {
newCol = newCol - number;
} else {
checkLives();
}
}
break;
case RIGHT_MOVE_CHAR:
if (lives == 1) {
newCol++;
} else if (lives > 1) {
squareNumberPrompt();
int number = keyBoard.nextInt();
if (number <= lives) {
newCol = newCol + number;
} else {
checkLives();
}
}
break;
case UNDO_MOVE_CHAR:
if (movement.size() > 1) {
movement.remove(movement.size() - 1);
System.out.println("The decreasing size of the arraylist is now " + movement.size()); //Test Line
} else if (movement.size() < 1) {
System.out.println("There is no move to be undone!");
}
break;
}
if (newRow < 0 || newRow >= BOARD_SIZE || newCol < 0 || newCol >= BOARD_SIZE) {
System.out.println("Sorry that move takes you off the board!");
} else {
char dest = board[newRow][newCol];
if (dest == WALL_CHAR) {
System.out.println("Sorry you landed on a wall!");
} else {
nbrMoves++;
if (dest == DOUGHNUT_CHAR) {
doughnutCheck = true;
nbrDoughnuts++;
doughnutLives++;
lives = (doughnutLives + 1);
}
board[playerRow][playerCol] = FREE_SQUARE_CHAR;
playerCol = newCol;
playerRow = newRow;
board[playerRow][playerCol] = PLAYER_CHAR;
}
}
movement.add(new Move(playerCol, playerRow, newCol, newRow, doughnutCheck));
System.out.println("The increasing size of the arraylist is now " + movement.size()); //Test Line
}
public static void squareNumberPrompt() {
System.out.println("Enter the number of squares to be moved");
}
public static void checkLives() {
System.out.println("Invalid number! The number must be"
+ " equal to or less than the number of lives you have");
}
}
答案 0 :(得分：0)
if (movement.size() > 1) {
movement.remove(movement.size() - 1);
System.out.println("The decreasing size of the arraylist is now " + movement.size()); //Test Line
} else if (movement.size() < 1) {
System.out.println("There is no move to be undone!");
}
您不会在move.size（）== 1时考虑到这一点，这可能是您的问题所在。
答案 1 :(得分：0)
运行代码后，我想我知道这个问题。撤消移动时，将删除ArrayList中的最后一个移动。但问题是，您将撤销视为移动本身。因此，当您撤消，然后再次撤消时，您可以撤消＆＃34;之前的撤消。例如，撤消后此控制台输出显示您如何增加回三个移动：
Next option ? Z // Do undo
The decreasing size of the arraylist is now 2 // The old move is undone
The increasing size of the arraylist is now 3 // However, the undo is counted as a move
那么，随后的撤销调用只会反复重复，撤消你的撤消，然后再添加它们，基本上陷入循环。要解决此问题，只需更改
即可movement.add(new Move(playerCol, playerRow, newCol, newRow, doughnutCheck));
使用if语句检查撤消移动并阻止它被添加到数组中，如下所示：
if (moveChar != UNDO_MOVE_CHAR)
movement.add(new Move(playerCol, playerRow, newCol, newRow, doughnutCheck));
编辑：另请参阅@ user7254424的回答，因为他是您遇到问题的另一个原因。