Here you can find the source of interButtonSpace()
public static Component interButtonSpace()
//package com.java2s; // Licensed under the Apache License, Version 2.0 (the "License"); import java.awt.Component; import javax.swing.Box; public class Main { /**//from w w w . j a v a 2s . com * An "inter-component" horizontal space, also used as the standard * inset from a frame to its content. This is the nominal "Em" space. */ public final static int STANDARD_SPACE = 12; /** * A horizontal strut between buttons on the same line. */ public static Component interButtonSpace() { return Box.createHorizontalStrut(STANDARD_SPACE); } }