java - 有没有办法使用 for 循环确定要在页面上绘制的确切行数？

Question

//**************************************************************************
// PP 6.11
//
// Design and implement a program that draws 20 horizontal, evenly spaced
// parallel lines of random length.
//**************************************************************************


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

public class PP6_11
{
    public static void main (String[] args)
    {
        JFrame frame = new JFrame ("Lines");
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

        LinesPanel panel = new LinesPanel();

        frame.getContentPane().add(panel);
        frame.pack();
        frame.setVisible(true);
    }
}

class LinesPanel extends JPanel
{
    private final int WIDTH = 400,HEIGHT = 300, LENGTH = WIDTH / 2;
    private final int SPACE = HEIGHT / 20, NUM_LINES = 20;
    private Random generator;

我已经完成了作业，效果很好。编译并运行时，代码绘制了 20 行，因为我使用了“SPACE”变量。我想知道是否有任何方法可以通过使用“NUM_LINES”变量来告诉程序我想要它绘制多少条线。

    //-----------------------------------------------------------------------
    // Sets up the drawing panel.
    //-----------------------------------------------------------------------

    public LinesPanel()
    {
        generator = new Random();

        setBackground (Color.black);
        setPreferredSize (new Dimension (WIDTH, HEIGHT));
    }

    //-----------------------------------------------------------------------
    // Paints evenly spaced Horizontal lines of random length.
    // lines that are half the width are highlighted with a re color.
    //-----------------------------------------------------------------------

    public void paintComponent (Graphics page)
    {

每次我尝试在 for 循环中使用 NUM_LINES = 20 和 SPACE = 20 变量时，它只绘制几行。这是我之前使用的 for 循环“for(int i = 0; i <= NUM​​_LINES; i += SPACE)”

        for (int i = 0; i <= HEIGHT; i += SPACE)
        {
            int y = generator.nextInt(WIDTH) + 1;

            if (y <= LENGTH)
            {
                page.setColor(Color.red);
                page.drawLine(0,i,y,i);
            }
            else
            {
                page.setColor(Color.blue);
                page.drawLine (0,i,y,i);
            }
        }


    }



}

有没有办法确定我画了多少条线并均匀地间隔它，或者我这样做的方式是最好的方法吗？

Answer 1

简单的答案是将 for 循环更改为:

for (int i = 0; i < HEIGHT; i += (HEIGHT - 1) / (NUM_LINES - 1))

请注意，我已经更改了比较以排除等于(因为高度实际上在您的窗口之外)，并且我们动态计算线之间的距离。

从高度中减去可以纠正我们的线位于从零开始的坐标系中的事实。 NUM_LINES 的减法根据第一条线绘制为零的事实进行调整。请注意，您的解决方案并未考虑最后一个因素，但恰好“有效”，因为您在屏幕外绘制了最后一行。如果您将 HEIGHT 更改为 401，您实际上会看到 21 行。

这是一个更好的实现，它考虑了许多因素，例如重绘高度和行间距的奇数倍，以及实际的面板尺寸。它还将线条垂直居中，以更加美观。

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

public class PP6_11
{
    public static void main (String[] args)
    {
        JFrame frame = new JFrame ("Lines");
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

        LinesPanel panel = new LinesPanel(20, 0.5);
        panel.setPreferredSize (new Dimension (400, 300));

        frame.getContentPane().add(panel);
        frame.pack();
        frame.setVisible(true);
    }
}

class LinesPanel extends JPanel
{
    private final int numLines;
    private final double colorSplit;
    private final Random generator;

    //-----------------------------------------------------------------------
    // Sets up the drawing panel.
    //-----------------------------------------------------------------------

    public LinesPanel(int numLines, double colorSplit)
    {
        this.numLines = numLines;
        this.colorSplit = colorSplit;

        this.generator = new Random();

        setBackground (Color.black);
    }

    //-----------------------------------------------------------------------
    // Paints evenly spaced Horizontal lines of random length.
    // lines that are half the width are highlighted with a re color.
    //-----------------------------------------------------------------------

    public void paintComponent (Graphics page)
    {
        // Clear the off-screen bitmap and set the background.
        super.paintComponent(page);

        final int pageWidth = getWidth();
        final int pageHeight = getHeight();

        // Calculate the line spacing and center vertically.
        final int lineSpace = (pageHeight - 1) / (numLines - 1);
        final int margin = (pageHeight - (lineSpace * (numLines - 1))) / 2;

            final int splitWidth = (int)(pageWidth * colorSplit);

        for (int y = margin; y < pageHeight; y += lineSpace)
        {
            int width = generator.nextInt(pageWidth) + 1;
            page.setColor(width <= splitWidth ? Color.red : Color.blue);
            page.drawLine(0, y, width, y);
        }
    }
}