Java tutorial
//package com.java2s; /** * Copyright (C) 2014-2017 Philip Helger (www.helger.com) * philip[at]helger[dot]com * * Licensed 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.Collection; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.function.Predicate; import javax.annotation.Nullable; public class Main { @Nullable public static <ELEMENTTYPE> ELEMENTTYPE findFirst(@Nullable final Iterable<? extends ELEMENTTYPE> aCollection, @Nullable final Predicate<? super ELEMENTTYPE> aFilter) { return findFirst(aCollection, aFilter, (ELEMENTTYPE) null); } @Nullable public static <ELEMENTTYPE> ELEMENTTYPE findFirst(@Nullable final Iterable<? extends ELEMENTTYPE> aCollection, @Nullable final Predicate<? super ELEMENTTYPE> aFilter, @Nullable final ELEMENTTYPE aDefault) { if (aFilter == null) return getFirstElement(aCollection); if (isNotEmpty(aCollection)) for (final ELEMENTTYPE aElement : aCollection) if (aFilter.test(aElement)) return aElement; return aDefault; } /** * Get the first element of the passed list. * * @param <ELEMENTTYPE> * List element type * @param aList * The list. May be <code>null</code>. * @return <code>null</code> if the list is <code>null</code> or empty, the * first element otherwise. */ @Nullable public static <ELEMENTTYPE> ELEMENTTYPE getFirstElement(@Nullable final List<ELEMENTTYPE> aList) { return isEmpty(aList) ? null : aList.get(0); } /** * Get the first element of the passed collection. * * @param <ELEMENTTYPE> * Collection element type * @param aCollection * The collection. May be <code>null</code>. * @return <code>null</code> if the collection is <code>null</code> or empty, * the first element otherwise. */ @Nullable public static <ELEMENTTYPE> ELEMENTTYPE getFirstElement(@Nullable final Collection<ELEMENTTYPE> aCollection) { return isEmpty(aCollection) ? null : aCollection.iterator().next(); } /** * Get the first element of the passed iterable. * * @param <ELEMENTTYPE> * Iterable element type * @param aIterable * The iterable. May be <code>null</code>. * @return <code>null</code> if the iterable is <code>null</code> or empty, * the first element otherwise. */ @Nullable public static <ELEMENTTYPE> ELEMENTTYPE getFirstElement(@Nullable final Iterable<ELEMENTTYPE> aIterable) { if (aIterable == null) return null; final Iterator<ELEMENTTYPE> it = aIterable.iterator(); return it.hasNext() ? it.next() : null; } public static boolean isNotEmpty(@Nullable final Iterable<?> aCont) { return aCont != null && aCont.iterator().hasNext(); } public static boolean isNotEmpty(@Nullable final Collection<?> aCont) { return aCont != null && !aCont.isEmpty(); } public static boolean isNotEmpty(@Nullable final Map<?, ?> aCont) { return aCont != null && !aCont.isEmpty(); } public static boolean isEmpty(@Nullable final Iterable<?> aCont) { return aCont == null || !aCont.iterator().hasNext(); } public static boolean isEmpty(@Nullable final Collection<?> aCont) { return aCont == null || aCont.isEmpty(); } public static boolean isEmpty(@Nullable final Map<?, ?> aCont) { return aCont == null || aCont.isEmpty(); } }