Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * 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. */ import java.util.ArrayList; import java.util.Collection; import java.util.Iterator; import java.util.List; public class Main { /** * <p>Joins the elements of the provided <code>Collection</code> into * a single String containing the provided elements.</p> * * <p>No delimiter is added before or after the list. * A <code>null</code> separator is the same as an empty String ("").</p> * * <p>See the examples here: {@link #join(Object[],String)}. </p> * * @param collection the <code>Collection</code> of values to join together, may be null * @param separator the separator character to use, null treated as "" * @return the joined String, <code>null</code> if null iterator input * @since 2.3 */ public static String join(Collection collection, String separator) { if (collection == null) { return null; } return join(collection.iterator(), separator); } /** * <p>Joins the elements of the provided <code>Iterator</code> into * a single String containing the provided elements.</p> * * <p>No delimiter is added before or after the list. * A <code>null</code> separator is the same as an empty String ("").</p> * * <p>See the examples here: {@link #join(Object[],String)}. </p> * * @param iterator the <code>Iterator</code> of values to join together, may be null * @param separator the separator character to use, null treated as "" * @return the joined String, <code>null</code> if null iterator input */ public static String join(Iterator iterator, String separator) { // handle null, zero and one elements before building a buffer if (iterator == null) { return null; } if (!iterator.hasNext()) { return ""; } Object first = iterator.next(); if (!iterator.hasNext()) { return toString(first); } // two or more elements StringBuffer buf = new StringBuffer(256); // Java default is 16, probably too small if (first != null) { buf.append(first); } while (iterator.hasNext()) { if (separator != null) { buf.append(separator); } Object obj = iterator.next(); if (obj != null) { buf.append(obj); } } return buf.toString(); } // ToString //----------------------------------------------------------------------- /** * <p>Gets the <code>toString</code> of an <code>Object</code> returning * an empty string ("") if <code>null</code> input.</p> * * <pre> * ObjectUtils.toString(null) = "" * ObjectUtils.toString("") = "" * ObjectUtils.toString("bat") = "bat" * ObjectUtils.toString(Boolean.TRUE) = "true" * </pre> * * @see StringUtils#defaultString(String) * @see String#valueOf(Object) * @param obj the Object to <code>toString</code>, may be null * @return the passed in Object's toString, or nullStr if <code>null</code> input * @since 2.0 */ public static String toString(Object obj) { return obj == null ? "" : obj.toString(); } }