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

public class Example extends JFrame{
    public static ImageIcon exampleImage=new ImageIcon(Example.class.getResource("thu.jpg"));
    JLabel exIL = new JLabel();
    JPanel jPanel = new JPanel();
    JLabel egL = new JLabel();

    public void eIinit(){
        exIL.setText("");
        exIL.setIcon(exampleImage);
        egL.setText("example for set the spectrums");
        jPanel.add(egL,BorderLayout.NORTH);
        jPanel.add(exIL,BorderLayout.SOUTH);
        getContentPane().setLayout(new FlowLayout());
        getContentPane().add(jPanel);

    }

    public  Example(){
//        super();
        eIinit();

    }

    public static void main(String args[]){
        Example f = new Example();
        f.pack();
        f.setVisible(true);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

}

------解决方案--------------------
public void example() 加了一个void就变成普通的方法了