Java: Graphics2D

Question

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

public class SimpleGui3C implements ActionListener {

JFrame frame;

public static void main(String[] args) {

    SimpleGui3C gui = new SimpleGui3C();
    gui.go();
}

public void go() {

    frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JButton button = new JButton("Change Colors");
    button.addActionListener(this);

    MyDrawPanel drawPanel = new MyDrawPanel();

    frame.getContentPane().add(BorderLayout.SOUTH, button);
    frame.getContentPane().add(BorderLayout.CENTER, drawPanel);
    frame.setSize(300, 300);
    frame.setVisible(true);
}
public void actionPerformed(ActionEvent event) {
    frame.repaint();
}
}

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

class MyDrawPanel extends JPanel {

public void paintComponet(Graphics g) {

    Graphics2D g2d = (Graphics2D) g;

    int red = (int) (Math.random() * 256);
    int green = (int) (Math.random() * 256);
    int blue = (int) (Math.random() * 256);
    Color startColor = new Color(red, green, blue);

    red = (int) (Math.random() * 256);
    green = (int) (Math.random() * 256);
    blue = (int) (Math.random() * 256);
    Color endColor = new Color(red, green, blue);

    GradientPaint gradient = new GradientPaint(70, 70, startColor, 150, 150, endColor);
    g2d.setPaint(gradient);
    g2d.fillOval(70, 70, 100, 100);

}
}

所以我已经连续两个小时尝试解决这个问题，但似乎无法解决问题。这个“程序”应该有一个椭圆形，并在屏幕底部出现一个按钮，允许我随机化椭圆形的颜色。我正在使用netbeans，每当我单击run时，我都会得到这样的结果：

有没有人能解决我的问题？如果这是一个愚蠢的问题，很抱歉浪费您的时间。

Answer 1

拼写很重要：paintComponet != paintComponent

总是在被覆盖的方法前面加上@Override。如果你这样做了，你的编译器会警告你你的错误。

因此，请更改以下内容：

public void paintComponet(Graphics g) {

    Graphics2D g2d = (Graphics2D) g;

    int red = (int) (Math.random() * 256);
    int green = (int) (Math.random() * 256);
    int blue = (int) (Math.random() * 256);
    Color startColor = new Color(red, green, blue);

    red = (int) (Math.random() * 256);
    green = (int) (Math.random() * 256);
    blue = (int) (Math.random() * 256);
    Color endColor = new Color(red, green, blue);

    GradientPaint gradient = new GradientPaint(70, 70, startColor, 150, 150, endColor);
    g2d.setPaint(gradient);
    g2d.fillOval(70, 70, 100, 100);
}

要这样做：

@Override // don't forget this
protected void paintComponent(Graphics g) { // spelling matters. Also make it protected

    // !!!! don't forget this!
    super.paintComponent(g); // to have the JPanel do housekeeping painting

    Graphics2D g2d = (Graphics2D) g;

    int red = (int) (Math.random() * 256);
    int green = (int) (Math.random() * 256);
    int blue = (int) (Math.random() * 256);
    Color startColor = new Color(red, green, blue);

    red = (int) (Math.random() * 256);
    green = (int) (Math.random() * 256);
    blue = (int) (Math.random() * 256);
    Color endColor = new Color(red, green, blue);

    GradientPaint gradient = new GradientPaint(70, 70, startColor, 150, 150, endColor);
    g2d.setPaint(gradient);
    g2d.fillOval(70, 70, 100, 100);
}