Here you can find the source of treeSet(E... add)
public static <E> Set<E> treeSet(E... add)
//package com.java2s; /*/*from w ww . j ava 2 s . c o m*/ * CollectionUtil.java * * This file is part of SQL Workbench/J, http://www.sql-workbench.net * * Copyright 2002-2017, Thomas Kellerer * * Licensed under a modified Apache License, Version 2.0 * that restricts the use for certain governments. * You may not use this file except in compliance with the License. * You may obtain a copy of the License at. * * http://sql-workbench.net/manual/license.html * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. * * To contact the author please send an email to: support@sql-workbench.net * */ import java.util.Arrays; import java.util.Set; import java.util.TreeSet; public class Main { public static <E> Set<E> treeSet(E... add) { Set<E> result = new TreeSet<>(); if (add != null) { result.addAll(Arrays.asList(add)); } return result; } public static <E> Set<E> treeSet(Set<E> base, E... add) { Set<E> result = new TreeSet<>(); result.addAll(base); if (add != null) { result.addAll(Arrays.asList(add)); } return result; } }