初学者挥动递归 [英] Beginner swing recursion
问题描述
第一次在这里发帖。这个编程任务让我难以接受，代码如下：
import java.awt。*;
import javax.swing。*;
公共类HTree扩展JPanel {
private Color color = new Color（（int）（Math.random（）* 256），（int）（Math.random（ ）* 256），（int）（Math.random（）* 256））;
public void draw（Graphics g，int n，double sz，double x，double y）{
if（n == 0）return;
double x0 = x - sz / 2，x1 = x + sz / 2;
double y0 = y - sz / 2，y1 = y + sz / 2;
//绘制H
g.setColor（颜色）的3个线段;
g.drawLine（（int）x0，（int）y，（int）x1，（int）y）;
g.drawLine（（int）x0，（int）y0，（int）x0，（int）y1）;
g.drawLine（（int）x1，（int）y0，（int）x1，（int）y1）;
//以递归方式绘制4个半尺寸
// H-tree的顺序为n-1
g.setColor（color）;
draw（g，n-1，sz / 2，x0，y0）;
draw（g，n-1，sz / 2，x0，y1）;
draw（g，n-1，sz / 2，x1，y0）;
draw（g，n-1，sz / 2，x1，y1）;
repaint（）;
}
public void paintComponent（Graphics g）{
super.paintComponent（g）;
draw（g，3，.5，.5，.5）;
}
public static void main（String [] args）{
HTree h = new HTree（）;
JFrame application = new JFrame（HTree）;
application.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）;
application.add（h）;
application.setSize（1000,1000）;
application.setVisible（true）;
}
}
它编译正确，但在运行程序时我都是get是一个空的JFrame。我不太熟悉swing，但我认为问题是HTree构造函数是错误的，或者我可能需要在main中调用draw（），但不知道如何使用Graphics对象调用它。感谢任何帮助！谢谢！
一些观察结果：
-
使用相对于面板当前大小的整数坐标。
-
覆盖
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
/ **
* @see https://stackoverflow.com/a/37450393/230513
* /
公共类HTree {
private void display（）{
JFrame f = new JFrame（HTree）;
f.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）;
f.add（new Tree（））;
f.pack（）;
f.setLocationRelativeTo（null）;
f.setVisible（true）;
}
私有静态类树扩展JPanel {
私有最终颜色color = Color.getHSBColor（（float）Math.random（），1,1） ;
public void draw（Graphics g，int n，double sz，double x，double y）{
if（n == 0）{
return;
}
double x0 = x - sz / 2，x1 = x + sz / 2;
double y0 = y - sz / 2，y1 = y + sz / 2;
//绘制H
g.setColor（颜色）的3个线段;
g.drawLine（（int）x0，（int）y，（int）x1，（int）y）;
g.drawLine（（int）x0，（int）y0，（int）x0，（int）y1）;
g.drawLine（（int）x1，（int）y0，（int）x1，（int）y1）;
//以递归方式绘制4个半尺寸
// H-tree的顺序为n-1
g.setColor（color）;
draw（g，n - 1，sz / 2，x0，y0）;
draw（g，n - 1，sz / 2，x0，y1）;
draw（g，n - 1，sz / 2，x1，y0）;
draw（g，n - 1，sz / 2，x1，y1）;
}
@Override
public void paintComponent（Graphics g）{
super.paintComponent（g）;
draw（g，3，getWidth（）/ 2，getWidth（）/ 2，getHeight（）/ 2）;
}
@Override
public Dimension getPreferredSize（）{
return new Dimension（500,500）;
}
public static void main（String [] args）{
EventQueue.invokeLater（new HTree（）:: display）;
}
}
}
First time posting here. This programming assignment has me stumped, the code is as follows:
import java.awt.*; import javax.swing.*; public class HTree extends JPanel { private Color color = new Color((int)(Math.random() * 256), (int)(Math.random() * 256), (int)(Math.random() * 256)); public void draw(Graphics g, int n, double sz, double x, double y) { if (n == 0) return; double x0 = x - sz/2, x1 = x + sz/2; double y0 = y - sz/2, y1 = y + sz/2; // draw the 3 line segments of the H g.setColor(color); g.drawLine((int)x0, (int)y, (int)x1, (int)y); g.drawLine((int)x0, (int)y0, (int)x0, (int)y1); g.drawLine((int)x1, (int)y0, (int)x1, (int)y1); // recursively draw 4 half-size // H-trees of order n-1 g.setColor(color); draw(g, n-1, sz/2, x0, y0); draw(g, n-1, sz/2, x0, y1); draw(g, n-1, sz/2, x1, y0); draw(g, n-1, sz/2, x1, y1); repaint(); } public void paintComponent(Graphics g) { super.paintComponent(g); draw(g, 3, .5, .5, .5); } public static void main(String[] args) { HTree h = new HTree(); JFrame application = new JFrame("HTree"); application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); application.add(h); application.setSize(1000, 1000); application.setVisible(true); } }It compiles correctly, but when running the program all I get is an empty JFrame. I am not too familiar with swing, but I think the problem is that either the HTree constructor is wrong, or I may need to call draw() in main, but not sure how to call it with a Graphics object. Any help is appreciated, thank you!
解决方案Some observations:
Use integer coordinates relative to the panel's current size.
Override
getPreferredSize()to establish the initial geometry.Use
Color.getHSBColor()to get bright, saturated colors; consider creating a gamut of hues, selecting a different one at each level, for example.Construct and manipulate Swing GUI objects only on the event dispatch thread.
Consider using a
JSpinnerorJSliderto control recursion depth interactively, as suggested here and here.Don't invoke
repaint()recursively; use it to schedule a call to your implementation ofpaintComponent(), as when the recursion depth charges in response to some input.Consider using
setStroke()and rendering hints, as shown here.Consider using a
javax.swing.Timer, increasing the recursion depth by one level each time theActionListeneris called.
import java.awt.Color; import java.awt.Dimension; import java.awt.EventQueue; import java.awt.Graphics; import javax.swing.JFrame; import javax.swing.JPanel; /** * @see https://stackoverflow.com/a/37450393/230513 */ public class HTree { private void display() { JFrame f = new JFrame("HTree"); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.add(new Tree()); f.pack(); f.setLocationRelativeTo(null); f.setVisible(true); } private static class Tree extends JPanel { private final Color color = Color.getHSBColor((float) Math.random(), 1, 1); public void draw(Graphics g, int n, double sz, double x, double y) { if (n == 0) { return; } double x0 = x - sz / 2, x1 = x + sz / 2; double y0 = y - sz / 2, y1 = y + sz / 2; // draw the 3 line segments of the H g.setColor(color); g.drawLine((int) x0, (int) y, (int) x1, (int) y); g.drawLine((int) x0, (int) y0, (int) x0, (int) y1); g.drawLine((int) x1, (int) y0, (int) x1, (int) y1); // recursively draw 4 half-size // H-trees of order n-1 g.setColor(color); draw(g, n - 1, sz / 2, x0, y0); draw(g, n - 1, sz / 2, x0, y1); draw(g, n - 1, sz / 2, x1, y0); draw(g, n - 1, sz / 2, x1, y1); } @Override public void paintComponent(Graphics g) { super.paintComponent(g); draw(g, 3, getWidth() / 2, getWidth() / 2, getHeight() / 2); } @Override public Dimension getPreferredSize() { return new Dimension(500, 500); } public static void main(String[] args) { EventQueue.invokeLater(new HTree()::display); } } }这篇关于初学者挥动递归的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
