Java Box Layout (BoxLayout) - Example

getContentPane().setLayout(new BoxLayout(getContentPane(), BoxLayout.X_AXIS));
//or
getContentPane().setLayout(new BoxLayout(getContentPane(), BoxLayout.Y_AXIS));

JButton	btn1 = new JButton("Button 1");
btn1.setAlignmentX(Component.CENTER_ALIGNMENT);
getContentPane().add(btn1);

JButton btn2 = new JButton("Button 2");
btn2.setAlignmentX(Component.CENTER_ALIGNMENT);
getContentPane().add(btn2);

package com.java.myapp;

import java.awt.Component;
import java.awt.EventQueue;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.BoxLayout;

public class MyForm extends JFrame {

	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				MyForm frame = new MyForm();
				frame.setVisible(true);
			}
		});
	}

	/**
	 * Create the frame.
	 */
	public MyForm() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(100, 100, 450, 300);
		
		getContentPane().setLayout(new BoxLayout(getContentPane(), BoxLayout.X_AXIS));
		
		JButton	btn1 = new JButton("Button 1");
		btn1.setAlignmentX(Component.CENTER_ALIGNMENT);
		getContentPane().add(btn1);
		
		JButton btn2 = new JButton("Button 2");
		btn2.setAlignmentX(Component.CENTER_ALIGNMENT);
		getContentPane().add(btn2);
		
		JButton btn3 = new JButton("Button 3");
		btn3.setAlignmentX(Component.CENTER_ALIGNMENT);
		getContentPane().add(btn3);
		
		JButton btn4 = new JButton("Button 4");
		btn4.setAlignmentX(Component.CENTER_ALIGNMENT);
		getContentPane().add(btn4);

	}
	
}