Java SE (Java Platform, Standard Edition)

Hi dude, below the codes have five JButton and I want to print out 4 JButton per row. I try to make the fifth JButton to the second row by using setLoaction method but it doesn't work. Is there any idea?

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

public class Loc {
	private JFrame frame = new JFrame();
	private JPanel pnlItem = new JPanel();
	private JPanel pnlMain = new JPanel();
	
	ArrayList<JButton> btnsOpt = new ArrayList<JButton>();
	
	//Constructor
	public Loc() {
		Container contentPane = frame.getContentPane();
		contentPane.add(createMainPane());
		
		frame.pack();
		frame.setSize(800,600);
		frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
		frame.setResizable(false);
		frame.setVisible(true);
	}
	
	public JPanel createMainPane() {
		btnsOpt.add(new JButton("11111"));
		btnsOpt.add(new JButton("2"));
		btnsOpt.add(new JButton("3"));
		btnsOpt.add(new JButton("4"));
		btnsOpt.add(new JButton("5"));
		
    	int buttonWidth = 60;
		int buttonHeight = 35;
		int itemPerRow = 4;
		int nextX = 10;
		int nextY = 10;
		
		for(int i=0; i<btnsOpt.size(); i++) {
			btnsOpt.get(i).setLocation(new Point(nextX, nextY));
			btnsOpt.get(i).setPreferredSize(new Dimension(buttonWidth, buttonHeight));
			pnlItem.add(btnsOpt.get(i));
			
			nextX = nextX + buttonWidth + 10;
			
			if(i%itemPerRow == 0) {
				if(i!=0) {
					nextX = 0;
					nextY = nextY + buttonHeight + 10;
				}
			}
			System.out.println("nextX = "+nextX);
			System.out.println("nextY = "+nextY);
		}
		pnlMain.add(pnlItem);
		
		return pnlMain;
	}
	
	public static void main(String args[]) {
		javax.swing.SwingUtilities.invokeLater(new Runnable() {
			public void run() {
				new Loc();
			}
		});
	}
}