java - 为什么 .setColor(,,,) 说无法在此程序中找到符号？

Question

当我运行此程序时，代码 g2.setColor(fillColor) 出现找不到符号错误。这是一个遗留问题吗？代码不正确？

I typed this code in verbatim from page165 of the book "Big Java" by Cay Horstmann

import java.applet.Applet;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import javax.swing.JOptionPane;

/**
 * An applet that lets a user choose a color by specifying the fractions of 
 * red, green, and blue.
 */
    public class ColorApplet extends Applet
    {
        public ColorApplet()
        {
            String input;

            //Ask user for red, green, blue values
            input = JOptionPane.showInputDialog("red: ");
            float red = Float.parseFloat(input);

            input = JOptionPane.showInputDialog("green: ");
            float green = Float.parseFloat(input);

            input = JOptionPane.showInputDialog("blue :");
            float blue = Float.parseFloat(input);

            //creates the color based on the RGB inputted values
            Color fillColor= new Color(red, green, blue);
        }

        public void paint(Graphics g)
        {
            Graphics2D g2= (Graphics2D)g;

            g2.setColor(fillColor);

            Rectangle square = new Rectangle((getWidth() - SQUARE_LENGTH)/2, 
            (getHeight() - SQUARE_LENGTH)/2, SQUARE_LENGTH, SQUARE_LENGTH);

            g2.fill(square);
        }

        private static final int SQUARE_LENGTH = 100;
    }

Answer 1

fillColor 未在 paint 方法中声明。在您的程序中 fillColor 仅在构造函数中具有其作用域 Color fillColor= new Color(red, green, blue);

您可以将其设为实例变量以使其可访问，例如:

public class ColorApplet extends Applet
{
   Color fillColor;

// now in constructor
public ColorApplet()
{
...
...
 fillColor= new Color(red, green, blue);
}

现在您可以在 paint 方法中使用 fillColor