如何在JOptionPane中更改默认的java徽标

Question

我想知道如何更改JOptionPane框的图标（标题栏中的java徽标）。我正在使用摇摆界面。请参阅下面的示例代码。想知道为什么每次我运行代码时，它总是显示java徽标图标而不是信息消息图标。

import javax.swing.JOptionPane;

public class NewClass
{

    public static void main(String[] args)
    {
        double width, length, area, perimeter;

        String lengthStr, widthStr, outputStr;

        lengthStr = JOptionPane.showInputDialog("Enter the length: ");
        length = Double.parseDouble(lengthStr);

        widthStr = JOptionPane.showInputDialog("Enter the width: ");
        width = Double.parseDouble(widthStr);

        area = length * width;
        perimeter = 2 * (length + width);

        outputStr = "Length: " + length + "\n" + "Width: " + width + "\n" + "Area: " + area + " square units\n" 
                + "Perimeter: " + perimeter + " units\n"; 

       JOptionPane.showMessageDialog(null, outputStr, "Rectangle", JOptionPane.INFORMATION_MESSAGE);         

       System.exit(0);

    }
}