Question

所以我有一个挑战，就是在applet中制作一个这样的螺旋形画。问题是，我是Java的新手，并且完全不知道如何让任何组件出现在屏幕上。我希望有人可以添加额外的代码来解决这个问题，不过我真的很感激任何答案：）

import javax.swing.JApplet;
import javax.swing.JOptionPane;
import javax.swing.JTextField;

import java.awt.BorderLayout;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.Dimension;
import java.awt.Toolkit;


public class SpaceCadets3_WB extends JApplet {

int numOfPoints = 1080;
int[] x = new int[numOfPoints];
int[] y = new int[numOfPoints];
int x1, x2, y1, y2, width, height, animationSleep = 0;
int R = 75;
int r = 10;
int O = 75;
JTextField changeNumOfPoints = new JTextField(15);

public SpaceCadets3_WB() {

}

public void start() {
    this.setSize(600, 600);
    this.setBackground(new Color(100,100,255));
    this.getContentPane().setLayout(null);
    this.getContentPane().add(changeNumOfPoints);
    changeNumOfPoints.setVisible(true);
    changeNumOfPoints.setLocation(width - changeNumOfPoints.getSize().width - 25, 25);
    }

public void calculatePoints(){
    width = SpaceCadets3_WB.this.getWidth();
    height = SpaceCadets3_WB.this.getHeight();
    for(int t = 0; t<numOfPoints; t++){
        x[t] = (int) ((R+r)*Math.cos(t) - (r+O)*Math.cos(((R+r)/r)*t) + width/2);
        y[t] = (int) ((R+r)*Math.sin(t) - (r+O)*Math.sin(((R+r)/r)*t) + height/2);
    }
}

public void paint(Graphics g){
    g.setColor(Color.RED);
    calculatePoints();
    for(int i = 0; i<numOfPoints;i++){
        x1 = x[i];
        x2 = x[i+1];
        y1 = y[i];
        y2 = y[i+1];
        g.drawLine(x1, y1, x2, y2);

        try {
            Thread.sleep(animationSleep);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
}
}

Answer 1

你在睡觉的方法，你应该从不做的事情。在Swing事件线程上调用Thread.sleep(...)是不好的，但在任何绘制方法中执行它都是一种罪过。所以现在小程序无法绘制。请记住，除了绘画之外，任何绘画方法都必须做什么，而且必须非常快速地完成。它不应该做任何程序逻辑，它不应该直接做动画，它应该只是绘画。使用Swing计时器，因为任何类似的问题都会告诉你如何做。

此外，永远不要直接在applet中绘制，而是在applet所持有的JPanel的paintComponent方法中绘制。

因此，创建JPanel，覆盖其paintComponent方法，并使用该类的字段进行绘制。然后更改Timer中这些字段的状态，并在JPanel上调用repaint（）。

修改是的，您应该避免使用空布局，因为这会阻止您轻松，充分地向GUI添加组件。相反，在这种情况下，FlowLayout（JPanel的默认布局）可以很好地工作。

例如：

import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Point; import java.awt.RenderingHints; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.image.BufferedImage; import java.beans.PropertyChangeEvent; import java.beans.PropertyChangeListener; import java.lang.reflect.InvocationTargetException; import java.util.concurrent.ExecutionException; import javax.swing.*; @SuppressWarnings("serial") public class SpaceCadets extends JApplet { @Override public void init() { try { SwingUtilities.invokeAndWait(new Runnable() { public void run() { SpaceCadetsPanel panel = new SpaceCadetsPanel(); getContentPane().add(panel); setSize(SpaceCadetsPanel.PREF_W, SpaceCadetsPanel.PREF_H); } }); } catch (InvocationTargetException | InterruptedException e) { e.printStackTrace(); } } } @SuppressWarnings("serial") class SpaceCadetsPanel extends JPanel { public static final int PREF_W = 600; public static final int PREF_H = 600; public final static int TOTAL_POINTS = 1080; private static final int R = 75; private static final int R2 = 10; private static final int O = 75; private static final Color DRAW_COLOR = Color.RED; private static final int ANIMATION_DELAY = 20; private Point[] pts; private JSpinner pointCountSpinner = new JSpinner(new SpinnerNumberModel( 800, 100, 1080, 1)); private JButton doItButton = new JButton(new DoItBtnAction("Do It!")); private BufferedImage bufImg = new BufferedImage(PREF_W, PREF_H, BufferedImage.TYPE_INT_ARGB); private Timer timer; public int imageIndex; private CalcWorker calcWorker; public Graphics2D g2; public SpaceCadetsPanel() { System.out.println(pointCountSpinner.getEditor().getClass()); add(pointCountSpinner); add(doItButton); setBackground(Color.white); } @Override public Dimension getPreferredSize() { if (isPreferredSizeSet()) { return super.getPreferredSize(); } return new Dimension(PREF_W, PREF_H); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); if (bufImg != null) { g.drawImage(bufImg, 0, 0, this); } } class DoItBtnAction extends AbstractAction { public DoItBtnAction(String name) { super(name); int mnemonic = (int) name.charAt(0); putValue(MNEMONIC_KEY, mnemonic); } @Override public void actionPerformed(ActionEvent e) { imageIndex = 0; if (timer != null && timer.isRunning()) { timer.stop(); } if (g2 != null) { g2.dispose(); } pts = new Point[0]; bufImg = new BufferedImage(PREF_W, PREF_H, BufferedImage.TYPE_INT_ARGB); g2 = bufImg.createGraphics(); g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g2.setColor(DRAW_COLOR); int totalPoints = 0; totalPoints = ((Integer) pointCountSpinner.getValue()).intValue(); timer = new Timer(ANIMATION_DELAY, new TimerListener(totalPoints)); calcWorker = new CalcWorker(totalPoints); calcWorker.addPropertyChangeListener(new CalcWorkerListener()); calcWorker.execute(); } } class CalcWorker extends SwingWorker<Point[], Void> { private int totalPoints; public CalcWorker(int totalPoints) { this.totalPoints = totalPoints; } @Override protected Point[] doInBackground() throws Exception { Point[] pts2 = new Point[totalPoints]; for (int i = 0; i < pts2.length; i++) { int x = (int) ((R + R2) * Math.cos(i) - (R2 + O) * Math.cos(((R + R2) / R2) * i) + PREF_W / 2); int y = (int) ((R + R2) * Math.sin(i) - (R2 + O) * Math.sin(((R + R2) / R2) * i) + PREF_H / 2); pts2[i] = new Point(x, y); } return pts2; } } class CalcWorkerListener implements PropertyChangeListener { @Override public void propertyChange(PropertyChangeEvent evt) { if (SwingWorker.StateValue.DONE == evt.getNewValue()) { try { pts = calcWorker.get(); timer.start(); } catch (InterruptedException | ExecutionException e) { e.printStackTrace(); } } } } class TimerListener implements ActionListener { private int totalPoints; public TimerListener(int totalPoints) { this.totalPoints = totalPoints; } @Override public void actionPerformed(ActionEvent e) { int x1 = pts[imageIndex].x; int y1 = pts[imageIndex].y; int x2 = pts[imageIndex + 1].x; int y2 = pts[imageIndex + 1].y; g2.drawLine(x1, y1, x2, y2); repaint(); imageIndex++; if (imageIndex == totalPoints - 1) { ((Timer) e.getSource()).stop(); } } } }

显示为，

Java JApplet：为什么我的组件出现在屏幕上？

1 个答案: