Java tutorial
//package com.java2s; import java.util.ArrayList; import java.util.List; public class Main { /** * Adds the element parameter only if it isn't inside yet. * * @param aList * The {@link List} to fill. * @param element * The element to add to the aList parameter. */ public static void addWhenNecessary(List aList, Object element) { if (aList == null) { aList = new ArrayList(); aList.add(element); return; } if (!aList.contains(element)) { aList.add(element); } } }