我继续创建了一个可运行的示例来说明您的要求。我不得不对你的课做一些假设。
这是输出。

ABCDEFGH
 1 .X.X.X.X  1
 2 ........  2
 3 ........  3
 4 ........  4
 5 ........  5
 6 ........  6
 7 ........  7
 8 ....Y...  8
   ABCDEFGH

下面是一个可运行的示例。我会在代码之后解释我的推理。

package com.ggl.testing;

import java.util.ArrayList;
import java.util.List;

public class GameBoard {

    private static String[] playerXCoordinates = 
        {"B1", "D1", "F1", "H1"};

    private static String[] playerYCoordinates = 
        {"E8"};

    public static void main(String[] args) {
        GameBoard gameBoard = new GameBoard(8, 8);
        gameBoard.setPlayersX(playerXCoordinates);
        gameBoard.setPlayersY(playerYCoordinates);
        System.out.println(gameBoard.toString());
    }

    private int width, height;

    private List<String> playersX;
    private List<String> playersY;

    public GameBoard(int width, int height) {
        this.width = width;
        this.height = height;
        this.playersX = new ArrayList<String>();
        this.playersY = new ArrayList<String>();
    }

    public void setPlayersX(String[] players) {
        for (int i = 0; i < players.length; i++) {
            playersX.add(players[i]);
        }
    }

    public void setPlayersY(String[] players) {
        for (int i = 0; i < players.length; i++) {
            playersY.add(players[i]);
        }
    }

    @Override
    public String toString() {
        String newLine = System.lineSeparator();
        StringBuilder builder = new StringBuilder();
        builder.append(createAlphaLine());
        builder.append(newLine);
        for (int i = 0; i < height; i++) {
            builder.append(createBoardLine(i + 1));
            builder.append(newLine);
        }
        builder.append(createAlphaLine());
        return builder.toString();
    }

    private StringBuilder createAlphaLine() {
        StringBuilder builder = new StringBuilder();
        builder.append("   ");
        for (int i = 0; i < width; i++) {
            char c = (char) (i + 'A');
            builder.append(c);
        }
        return builder;
    }

    private StringBuilder createBoardLine(int index) {
        StringBuilder builder = new StringBuilder();
        builder.append(String.format("%2d", index));
        builder.append(" ");
        for (int i = 0; i < width; i++) {
            char c = (char) (i + 'A');
            String s = Character.toString(c) + index;
            if (playersX.contains(s)) {
                builder.append("X");
            } else if (playersY.contains(s)) {
                builder.append("Y");
            } else {
                builder.append(".");
            }
        }
        builder.append(" ");
        builder.append(String.format("%2d", index));
        return builder;
    }

}

我一次创建一个类方法。
首先，我假设课堂上有一些输入。你对类的输入不是很清楚。
接下来，我建造了 toString 方法一次一部分。
我先做了字母表上的行。然后，当代码的这一部分起作用时，我就开始处理板上的行。首先，我做了行号。最后，我查了一下 Lists 确定要打印的字符。
分而治之。通常，你是通过上课来完成的。在这种情况下，我是用方法做的。一次编写一个方法，并测试每个方法。
分而治之。
编辑添加：只是为了好玩，这里是26 x 26板输出。

ABCDEFGHIJKLMNOPQRSTUVWXYZ
 1 .X.X.X.X..................  1
 2 ..........................  2
 3 ..........................  3
 4 ..........................  4
 5 ..........................  5
 6 ..........................  6
 7 ..........................  7
 8 ....Y.....................  8
 9 ..........................  9
10 .......................... 10
11 .......................... 11
12 .......................... 12
13 .......................... 13
14 .......................... 14
15 .......................... 15
16 .......................... 16
17 .......................... 17
18 .......................... 18
19 .......................... 19
20 .......................... 20
21 .......................... 21
22 .......................... 22
23 .......................... 23
24 .......................... 24
25 .......................... 25
26 .......................... 26
   ABCDEFGHIJKLMNOPQRSTUVWXYZ