Question

我正在尝试为我一直在努力的课程完成作业。我应该使用位置类，arraylist和2D阵列对抗计算机来构建战舰游戏。用户在5x5板上获得8次猜测。我正在接触下面的指示，所以它更清楚。

我目前正试图检查用户猜测（行，列形式）是否与存储在arraylist中的船舶的位置对象匹配，但是，无论您输入什么，它总是将其评估为其他，并标记它作为一个小姐（也就是在棋盘上放置一个X）。我做错了什么？

到目前为止，这是我的代码：

驱动程序类：

import java.util.Random; import java.util.Scanner; import java.util.ArrayList; 

public class battleshipDriver {

    public static void main(String[] args) {
        //fields
        char [][] board = new char[5][5]; // game board array
        ArrayList<Location> Location1 = new ArrayList<>(); // array list to hold location objects
        initialBoard(board); // prints initial board state
        Random computer = new Random(); //create num gen for computer placements
        int row, col;
        Scanner user = new Scanner(System.in);

        //stuff that is doing things
        //puts comp's placements in Location
        for(int i = 0; i <= 4; i ++) {
            row = computer.nextInt(5);
            col = computer.nextInt(5);
            Location battleship = new Location(row, col);
            Location1.add(battleship);
        }
        System.out.println(Location1);
        int turnsLeft = 8;
        int numShips = 4;
        do {
            System.out.println("You have " + turnsLeft + " turns left." + "\n"
                + "There are " + numShips + " ships left.");
            System.out.println("Please make a guess (row, column)");

            row = user.nextInt();
            col = user.nextInt();
            Location userGuess = new Location(row, col);

            if(row>4 || col>4 ) {
                System.out.println("Your move is invalid.");
            }

            else if (board[row][col] == 'X' || board[row][col] == '*') {
                System.out.println("You have already guessed that location");
            }
            for(Location loc: Location1) {
                if(Location1.contains(userGuess)) {
                    Location1.remove(userGuess);
                    board[row][col] = '*';
                    updateBoard(board);
                    System.out.println("You hit a ship");
                    break;
                }
                else {
                    board[row][col] = 'X';
                    updateBoard(board);
                    break;
                }
            }
        }while(turnsLeft != 0);

    }



    //printBoard method
    public static void initialBoard(char[][] board) {
        //for loops iterate through each 
        for(int row = 0; row< board.length; row++) { 
            for(int col = 0; col < board[row].length; col++) {
                board [row][col] = 'O'; //assigns O to signify open water 
                //(this may need to change. Most likely 
                //will always make the board O's only
                System.out.print(board[row][col] + " ");
            }
            System.out.println();
        }
    }
    public static void updateBoard(char[][] board) {
        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();
        }


    }
}

位置等级：

public class Location {
    private int row;
    private int col;

    //getters and setters
    public int getRow() {
        return row;
    }
    public int getCol() {
        return col;
    }

    public void setRow(int row) {
        this.row = row;
    }
    public void setCol(int col) {
        this.col = col;
    }

    //constructors 
    public Location(int row, int col) {
        this.row = row;
        this.col = col;

    }

    public String toString() {
        return  row + ", " + col ;
    }
}

我目前有数组列表打印其内容，以便我可以输入已知的发货地点，看看我是否正常工作。

Answer 1

Location类必须覆盖equals和ArrayList#contains(...)的hashCode才能工作。这是你的问题及其解决方案。

创建row和col final字段并使用它们来检查相等性并计算hashCode（你必须只使用不变量来执行此操作）。

类似的东西：

package pkg1;

public class Location {
    private final int row;
    private final int col;

    // getters and setters
    public int getRow() {
        return row;
    }

    public int getCol() {
        return col;
    }

    // make the field immutable!
    // public void setRow(int row) {
    // this.row = row;
    // }

    // make the field immutable!
    // public void setCol(int col) {
    // this.col = col;
    // }

    // constructors
    public Location(int row, int col) {
        this.row = row;
        this.col = col;

    }

    public String toString() {
        return row + ", " + col;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + col;
        result = prime * result + row;
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Location other = (Location) obj;
        if (col != other.col)
            return false;
        if (row != other.row)
            return false;
        return true;
    }
}

ArrayList API中的contains(...)方法条目：

如果此列表包含指定的元素，则返回true。更正式地说，当且仅当此列表包含至少一个元素e时才返回true（o == null？e == null：o.equals（e））。

如您所见，该方法使用.equals(...)方法检查包含。

使用arraylist的Java战舰：将用户输入与数组列表

1 个答案: