VS Code中Java程序仅能Debug运行，常规编译报错求助

编译错误信息 #

PS C:\Users\blake\Desktop\javavscode\BattleShip> javac Main.java
Main.java:10: error: cannot find symbol
        Board board = new Board(input);
        ^
  symbol:   class Board
  location: class Main
Main.java:10: error: cannot find symbol
        Board board = new Board(input);
                          ^
  symbol:   class Board
  location: class Main

代码内容 #

Main.java #

package BattleShip;

import java.util.Scanner;

public class Main{
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("What size do you want the board to be?: ");
        int input = Integer.valueOf(scanner.nextLine());
        Board board = new Board(input);
        board.print();

    }
}

Board.java #

package BattleShip;

public class Board {
    private char[][] board;
    private char water = '~';
    private int size;

    public Board(int size){
        this.size = size;
        this.board = new char[size][size];

        for (int i = 0; i < board.length; i++){
            for (int j = 0; j < board.length; j++){
                board[i][j] = water;
            }
        }
    }

    public void print(){
        for (int i = 0; i < board.length; i++){
            for (int j = 0; j < board.length; j++){
                System.out.print(board[i][j] + " ");
            }
            System.out.println("");
        }
    }
}

VS Code Debug运行命令 #

PS C:\Users\blake\Desktop\javavscode\BattleShip>  c:; cd 'c:\Users\blake\Desktop\javavscode'; & 'C:\Users\blake\AppData\Local\Programs\Eclipse Adoptium\jdk-17.0.7.7-hotspot\bin\java.exe' '-XX:+ShowCodeDetailsInExceptionMessages' '-cp' 'C:\Users\blake\AppData\Roaming\Code\User\workspaceStorage\b656ed2f78ffde906270d9c291aeeeb0\redhat.java\jdt_ws\javavscode_a7ed4f9c\bin' 'BattleShip.Main' What size do you want the board to be?:

疑问 #

目录中已生成Board.class和Main.class文件，请问是否需要使用这些文件运行程序？

解决办法 #

问题根源 #

你用了package BattleShip;声明包结构，但终端直接执行javac Main.java时，编译器只会编译Main.java，找不到同包的Board类（Board.java也需要编译，且文件要放在对应包目录下）。VS Code的Debug模式自动帮你处理了包结构和类路径，所以能正常运行。

正确编译与运行步骤 #

1. 确认目录结构：把Main.java和Board.java放在名为BattleShip的文件夹下（包名和文件夹名必须一致），上级目录是C:\Users\blake\Desktop\javavscode。
2. 编译代码：打开终端，切换到上级目录（cd C:\Users\blake\Desktop\javavscode），执行命令：

   javac BattleShip/*.java
   

   这会同时编译两个类，生成的.class文件会自动放在BattleShip文件夹里。
3. 运行程序：同样在上级目录，执行：

   java BattleShip.Main
   

关于已生成的.class文件 #

如果已经有Board.class和Main.class，只要它们在BattleShip文件夹下，直接在上级目录执行上面的java BattleShip.Main命令就能运行，不需要重新编译。别在BattleShip目录下运行，否则类路径会出错。

内容的提问来源于stack exchange，提问作者NATCHY