java - 为什么网格上的线条末端超出了该网格的给定宽度和高度？

Question

我正在尝试绘制一个网格。比如说，列 x 行是 5x6。我的问题是东部和南部的线结束超过给定的列和行值。它不大，也许只有一毫米，但仍然很烦人。我希望网格看起来像一个矩形，在上面的例子中，有 20 个单元格。我的代码中的错误在哪里？绘制这个有缺陷的网格的代码片段如下。谢谢!

package Main;

import java.awt.Dimension;

import javax.swing.JFrame;

public class GridMain {

    public static void main(String[] args) {
        JFrame jframe = new JFrame();
        jframe.setPreferredSize(new Dimension(640, 730));
        jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Mypanel mypanel = new Mypanel(5,6);
        jframe.add(mypanel);
        jframe.pack();
        jframe.setVisible(true);
    }
}
package Main;

import java.awt.Graphics;

import javax.swing.JPanel;

public class Mypanel extends JPanel {
    /**
 * 
 */
    private static final long serialVersionUID = 1L;
    private int height;
    private int width;
    private int gapBetweenPoints = 20;
    private int gapBetweenFrameAndGrid=15;
    public Mypanel(int columns, int rows) {
        width = columns;
        height = rows;
    }

    protected void paintComponent(Graphics g) {
        for (int i =0 ; i < height; i++) {
            g.drawLine(gapBetweenFrameAndGrid, i * gapBetweenPoints
                    + gapBetweenFrameAndGrid, width * gapBetweenPoints, i
                    * gapBetweenPoints + gapBetweenFrameAndGrid);
        }
        for (int i = 0; i < width; i++) {
            g.drawLine(i * gapBetweenPoints + gapBetweenFrameAndGrid,
                    gapBetweenFrameAndGrid, i * gapBetweenPoints +  gapBetweenFrameAndGrid,
                    height * gapBetweenPoints);
        }
    }
}

Answer 1

要小心你的出发点；我不会达到宽度(高度)，而只会达到宽度-1/高度-1。所以下面的代码:

    for (int i =0 ; i < height; i++) {
        g.drawLine(gapBetweenFrameAndGrid, i * gapBetweenPoints
                + gapBetweenFrameAndGrid, gapBetweenFrameAndGrid+(width-1) * gapBetweenPoints, i
                * gapBetweenPoints + gapBetweenFrameAndGrid);
    }
    for (int i = 0; i < width; i++) {
        g.drawLine(i * gapBetweenPoints + gapBetweenFrameAndGrid,
                gapBetweenFrameAndGrid, i * gapBetweenPoints +  gapBetweenFrameAndGrid,
                gapBetweenFrameAndGrid+(height-1) * gapBetweenPoints);
    }

一般情况

    for (int i =0 ; i < height; i++) {
        g.drawLine(startingX, i * gapBetweenPoints
                + gapBetweenFrameAndGrid, startingX+(width-1) * gapBetweenPoints, i
                * gapBetweenPoints + gapBetweenFrameAndGrid);
    }
    for (int i = 0; i < width; i++) {
        g.drawLine(i * gapBetweenPoints + gapBetweenFrameAndGrid,
                startingY, i * gapBetweenPoints +  gapBetweenFrameAndGrid,
                startingY+(height-1) * gapBetweenPoints);
    }