JLabel image won't show up

Hi! I'm just new at GUI programming and I've been busy creating a GUI for my project.

My image won't show up in this particular code. I've made two other classes and the images load perfectly.

import javax.swing.*;
import java.awt.image.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class Battle implements ActionListener{

    JFrame frame = new JFrame("Test");
    JPanel buttons, pic;
    JButton attack, attack1,attack2,attack3,attack4;
    JLabel label;
    JLabel grid[][];
public  Battle(){

        frame.setBounds(50, 50, 500, 500);
        pic = new JPanel();
        buttons = new JPanel();


        buttons.setLayout(new GridLayout(2,2));
        attack = new JButton("Attack");
        buttons.add(attack1 = new JButton("Attack1"));
        buttons.add(attack2 = new JButton("Attack2"));
        buttons.add(attack3 = new JButton("Attack3"));
        buttons.add(attack4 = new JButton("Attack4"));
        attack.setSize(30,40);
        frame.add(attack,BorderLayout.SOUTH);

        pic.setLayout(new GridLayout(2,2));
        frame.add(pic,BorderLayout.CENTER);
        grid = new JLabel[2][2];
        pic.add(grid[0][0]= new JLabel(new ImageIcon("agumon3.png")));


        attack.addActionListener(this);
        attack1.addActionListener(this);

        frame.pack();
        frame.setVisible(true);
    }
    public static void main(String args[]){
        new Battle();
    }
    public void actionPerformed(ActionEvent e){
        if(e.getSource()==attack){
            frame.remove(attack);
            frame.repaint();
            frame.add(buttons,BorderLayout.SOUTH);

        }
        else if(e.getSource()==attack1)
        {
            JOptionPane.showMessageDialog(null, "Meow attacks arf!");
            frame.remove(buttons);
            frame.repaint();
            frame.add(attack,BorderLayout.SOUTH);

        }
    }
}