java - Eclipse:Java，找不到主要方法

Question

我最近把我所有的代码都手动导入到 BlueJ 的一个 eclipse 项目中，然后我习惯了“运行配置”的设置，终于觉得我在家自由了。然后我运行代码，我得到了这个错误

java.lang.NoSuchMethodError: main
Exception in thread "main" 

所以我想我必须添加一个 main 方法(我从来没有在 BlueJ 中这样做过，为什么？)。所以我只是调用了构造函数方法(在 BlueJ 中，我只创建一个新对象，然后 JFrame 就会显示)。所以我这样做了，同样的错误。在尝试不同的事情(例如将构造函数中的代码移动到不同的方法等)之后。我只是把它放在主要方法中:

public void main(String[] args)
{
    System.out.println("Hello, this is main why won't Java find this.");
}

在那之后我仍然遇到同样的错误，所以我决定将它添加到我所有的类中以确保它没有使用另一个类作为主类。仍然是同样的错误，所以我来找你，想知道你们中是否有人遇到过这个问题。我也确实搜索了谷歌，我发现的只是 private 类等的问题，并且感觉我所有的类都是 public (嘿，我来自 Python :))。我知道那不是问题所在。请帮助:)

我的运行配置图片

这是我的主要方法代码

警告:很长

import java.awt.event.*;
import java.awt.*;
import javax.swing.*;

public class AppFrame extends JFrame
{

    public String status = "Status:";// Status of Applet
    public int paint_count = 1;// Number of times applet has been painted
    public int[] mousePos = {-1, -1};// Stores Mouse's Last Clicked X and Y Cordinates
    public int[] boardPos = {-1, -1};//Stores The Board's X and Y Cordinates
    public int[] selectedSquarePos = {-1, -1};

    public int[] boardSquare = {-1, -1};//Stores Last Clicked Square

    public Color P1_Color = Color.GRAY;
    public Color P2_Color = Color.WHITE;
    public Color SquareEven = Color.BLACK;
    public Color SquareOdd = Color.RED;// pieces move on this one

    public int boardHeight = 400;
    public int boardWidth = 400;

    public boolean pieceSelected = false;
    public boolean CheckersPiece = false;

    public Board CheckersBoard = new Board();

    public Image buffer = null;
    public Graphics bg = null;

    public void main(String[] args)
    {
        System.out.println("Hello, this is main why won't Java find this.");
    }
    public AppFrame()
    {
        super("JCheckers");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(900,900);
        setVisible(true);

        buffer = createImage(getWidth(), getHeight());
        boardHeight = getHeight() - 40; // 20 pixel border at top and bottom and 20 pixels for blue bar
        boardWidth = getWidth() - 40; // 20 pixel border at left and right
        bg = buffer.getGraphics();

        addMouseListener(new MouseAdapter()
        {
            public void mouseClicked (MouseEvent e)
            {
                handleClick(e);
            }
        }
        );
    }

    public void handleClick(MouseEvent e)
    {
        /* Handles tracking of mouse clicks; DOES NOT HANDLE DISPLAY, it just updates the data and calls redraw */
        mousePos[0] = e.getX();
        mousePos[1] = e.getY();
        repaint();
    }

    public void paint(Graphics g)
    {
        super.paint(g);
        render(g);
    }

    public void render(Graphics g)
    {   
        bg.clearRect(0,0, getWidth(), getHeight());

        //Draw Chess Board and Pieces
        renderChessBoard(bg, 20, 20);

        // Display Info
        System.out.println(status);
        System.out.println(String.format("Last Mouse Click @ (X:%d Y:%d)", mousePos[0], mousePos[1]) );
        System.out.println("Paint #" + paint_count );
        System.out.println(String.format("Board Square (x:%s, y:%s) %b", boardSquare[0], boardSquare[1], CheckersPiece) );
        System.out.println(CheckersBoard.status );
        paint_count += 1;
        // Draw Image to Screen
        g.drawImage(buffer, 0, 25, null);// so it does not get hidden by the blue close/min/max room

    }

    public boolean isValidSquare(int col, int row)
    {
        if (col > -1 & col < 8) {return true;}
        return false;
    }

    public void renderChessBoard(Graphics g, int x, int y)
    {
        /* Renders board and pieces*/
        // sense the row squares are well squares then the
        // board will be a square also; so we draw it with whatever
        // side is smallest, width or height
        boardPos[0] = x;
        boardPos[1] = y;

        drawBoard(g, x, y, boardWidth, boardHeight);
        boardSquare = getBoardSquare(mousePos[0], mousePos[1]);
        CheckersPiece = isCheckersPiece(boardSquare[0], boardSquare[1]);
        boolean validSquare = isValidSquare(boardSquare[0], boardSquare[1]);
        if (validSquare)
        {
            if (CheckersPiece)
            {
                selectSquare(g, boardSquare[0], boardSquare[1]);
            }
            else
            {
                if (pieceSelected)
                {
                    int selectedCol = selectedSquarePos[0];
                    int selectedRow = selectedSquarePos[1];
                    int toCol = boardSquare[0];
                    int toRow = boardSquare[1];

                    System.out.println(selectedCol + " " + selectedRow + " " + toCol + " " + toRow);
                    if (!CheckersBoard.move(selectedSquarePos, boardSquare)) // not a valid move;
                    {
                        pieceSelected = false;   
                    }
                }
            }
        }
        parseBoard(CheckersBoard.board, g);
    }

    public void drawBoard(Graphics g, int Bx, int By, int Bw, int Bh)
    {
        int numberRowsDrawed = 0;

        int rH = Bh / 8;
        int rW = Bw; // Row width is the same as the Board's width because the board and the row share the same sides

        while (numberRowsDrawed < 8)
        {

            int rY = (numberRowsDrawed * rH) + By;
            // Row X is the same as the Board X because the board and the row share the same sides
            int rX = Bx;

            Color EVEN = SquareEven;
            Color ODD = SquareOdd;
            // Yes Yes The EVEN Color is now odd and vica versa its because rows only now there row counts and so they start at 0 and don't
            // include the rows above
            if ((numberRowsDrawed % 2) != 0) {EVEN = SquareOdd; ODD = SquareEven;}

            drawRow(g, rX, rY, rW, rH, EVEN, ODD);
            numberRowsDrawed +=1;

        }

    }

    public void drawRow(Graphics g, int x, int y, int width, int height, Color EVEN, Color ODD)
    {   
        System.out.println("Board Y: " + y);
        int squareW = width / 8;
        int squareH = height;
        int numberSquaresCreated = 0;
        while (numberSquaresCreated < 8)
        {
            // needs a special case because Java's modulo uses division (so it would give a divide by 0 error) STUPID JAVA!!!!!!
            if (numberSquaresCreated == 0)
            {
                g.setColor(EVEN);
                g.fillRect(x, y, squareW, squareH);
            }
            else
            {
                if (numberSquaresCreated % 2 == 0){g.setColor(EVEN);}
                else {g.setColor(ODD);}
                int sX = x + (squareW * numberSquaresCreated);
                g.fillRect(sX, y, squareW, squareH);
            }
            numberSquaresCreated +=1;
        }
    }

    public void drawMan(Graphics g, int boardRow, int boardCol, Color pieceColor)
    {
        int x = boardPos[0];
        int y = boardPos[1];
        int pixelPosX = x + ((boardWidth / 8) * boardRow);
        int pixelPosY = y + ((boardHeight / 8) * boardCol);
        g.setColor(pieceColor);
        g.fillOval(pixelPosX + 13, pixelPosY + 13, (boardWidth / 8) - 26, (boardHeight / 8) - 26);
    }

   public void drawKing(Graphics g, int boardRow, int boardCol, Color pieceColor, Color crownColor)
   {
       drawMan(g, boardRow, boardCol, pieceColor);
       g.setColor(crownColor);
       int x = boardPos[0];
       int y = boardPos[1];
       double DsizeFactor = ( (float) boardHeight / 8.0) / 3.75;
       int sizeFactor = (int) DsizeFactor;
       int pixelPosX = x + ((boardWidth / 8) - sizeFactor) / 2 + ((boardWidth / 8) * boardRow);
       int pixelPosY = y + ((boardHeight / 8) - sizeFactor) / 2 + ((boardHeight / 8) * boardCol);
       int[] xPoints = {pixelPosX, pixelPosX,  pixelPosX + sizeFactor, pixelPosX + sizeFactor, pixelPosX + ((sizeFactor * 3) / 4), pixelPosX + (sizeFactor / 2),  pixelPosX + (sizeFactor / 4) };
       int[] yPoints = {pixelPosY, pixelPosY + sizeFactor, pixelPosY + sizeFactor, pixelPosY,  pixelPosY + (sizeFactor / 2), pixelPosY, pixelPosY + (sizeFactor / 2)};
       g.fillPolygon(xPoints, yPoints, 7);
   }

   public void selectSquare(Graphics g, int bSX, int bSY)
   {
       g.setColor(Color.YELLOW);
       /*+10 is to offset text (the xy cordinates are the bottom left side of the text NOT top left.*/
       pieceSelected = true;
       int squareX = boardPos[0] + (boardWidth / 8) * bSX;
       int squareY = 10 + boardPos[1] + (boardHeight / 8) * bSY;
       selectedSquarePos[0] = bSX;
       selectedSquarePos[1] = bSY;
       g.drawString("Selected", squareX, squareY);

   }

// Data Handling and Retreiving methods
    public void parseBoard(String[][] Board, Graphics g)
    {
        int row = 0;
        int col = 0;
        for (String[] rowOfPieces : Board)
        {
            for (String piece : rowOfPieces)
            {
                if (piece != "X")
                {   
                    Color PIECE_COLOR = P1_Color;
                    if (piece.contains("P2")) {PIECE_COLOR = P2_Color;}

                    if (piece.contains("C"))
                    {
                        drawMan(g, col, row, PIECE_COLOR);
                    }
                    if (piece.contains("K"))
                    {
                        Color Crown_Color = P2_Color;
                        if (PIECE_COLOR != P1_Color) {Crown_Color = P1_Color;}
                        drawKing(g, col, row, PIECE_COLOR, Crown_Color);
                    }
                }
                col+=1;
            }
            row +=1;
            col = 0;
        }
    }


    public int[] getBoardSquare(int x, int y)
    {   
        //row or col  =  boardpos - offset / row height or width
        if ((x < boardPos[0]) | (y < boardPos[1]) | (x > (boardPos[0] + boardWidth)) | (y > (boardPos[1] + boardHeight)) )
        {
            int[] BS = {-1, -1};
            return BS;
        }
        int col = (x - boardPos[0]) / (boardWidth / 8);
        int row = (y - boardPos[1]) / (boardHeight / 8);

        int[] BS = {col, row};
        return BS;
    }

    public boolean isCheckersPiece(int BoardSquareX, int BoardSquareY)
    {
        int Px = BoardSquareX;
        int Py = BoardSquareY;
        if (Px == -1 & Py == -1)
        {
            return false;
        }
        String Square = CheckersBoard.board[Py][Px];
        return Square != "X";

    }
}

Answer 1

你忘记了static:

public static void main(String[] args)

但为了真正启动您的应用程序，您应该从该方法启动它，而不仅仅是拥有它。以下是如何启动它:

public static void main(String[] args) {
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
       @Override
       public void run() {
           AppFrame frame = new AppFrame();
           frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       }
   });
}

请务必注意 EXIT_ON_CLOSE - 这将使 JVM 在您按下 X 按钮时退出。否则您的应用程序将继续运行，您甚至可能不会注意到。