Java ImageIcon/Icon 和 JLabel 不工作

为什么我的代码没有显示我插入的图像？没有编译错误或语法错误，但为什么会这样呢？

import java.awt.FlowLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.SwingConstants;

public class FirstUI extends JFrame{

    private JLabel firstlabel;
    private JLabel secondLabel;
    private JLabel pie;
    public FirstUI(){
        super("Tittle");
        setLayout(new FlowLayout());
        firstlabel = new JLabel("Hello World");
        firstlabel.setToolTipText("Hello World");

        String path = "pie.png";
        Icon pie = new ImageIcon(path);
        secondLabel = new JLabel("Text with icon",pie,SwingConstants.LEFT);
        add(secondLabel);
        add(firstlabel);
    }
}

主班

import javax.swing.JFrame;
public class FirstUiTest {

    public static void main(String[] args){

         FirstUI MyUI = new FirstUI();
         MyUI.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         MyUI.setSize(320,280);
         MyUI.setVisible(true);
    }
}

如果“pie.png”位于同一路径中FirstUI.class尝试使用：

Icon pie = new ImageIcon(ImageIO.read( FirstUI.class.getResourceAsStream( "pie.png" ) ) );