1 /* 2 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 package java.util; 26 27 import java.io.Serializable; 28 import java.util.function.BinaryOperator; 29 import java.util.function.Function; 30 import java.util.function.ToDoubleFunction; 31 import java.util.function.ToIntFunction; 32 import java.util.function.ToLongFunction; 33 34 /** 35 * Package private supporting class for {@link Comparator}. 36 */ 37 class Comparators { Comparators()38 private Comparators() { 39 throw new AssertionError("no instances"); 40 } 41 42 /** 43 * Compares {@link Comparable} objects in natural order. 44 * 45 * @see Comparable 46 */ 47 enum NaturalOrderComparator implements Comparator<Comparable<Object>> { 48 INSTANCE; 49 50 @Override compare(Comparable<Object> c1, Comparable<Object> c2)51 public int compare(Comparable<Object> c1, Comparable<Object> c2) { 52 return c1.compareTo(c2); 53 } 54 55 @Override reversed()56 public Comparator<Comparable<Object>> reversed() { 57 return Comparator.reverseOrder(); 58 } 59 } 60 61 /** 62 * Null-friendly comparators 63 */ 64 final static class NullComparator<T> implements Comparator<T>, Serializable { 65 private static final long serialVersionUID = -7569533591570686392L; 66 private final boolean nullFirst; 67 // if null, non-null Ts are considered equal 68 private final Comparator<T> real; 69 70 @SuppressWarnings("unchecked") NullComparator(boolean nullFirst, Comparator<? super T> real)71 NullComparator(boolean nullFirst, Comparator<? super T> real) { 72 this.nullFirst = nullFirst; 73 this.real = (Comparator<T>) real; 74 } 75 76 @Override compare(T a, T b)77 public int compare(T a, T b) { 78 if (a == null) { 79 return (b == null) ? 0 : (nullFirst ? -1 : 1); 80 } else if (b == null) { 81 return nullFirst ? 1: -1; 82 } else { 83 return (real == null) ? 0 : real.compare(a, b); 84 } 85 } 86 87 @Override thenComparing(Comparator<? super T> other)88 public Comparator<T> thenComparing(Comparator<? super T> other) { 89 Objects.requireNonNull(other); 90 return new NullComparator<>(nullFirst, real == null ? other : real.thenComparing(other)); 91 } 92 93 @Override reversed()94 public Comparator<T> reversed() { 95 return new NullComparator<>(!nullFirst, real == null ? null : real.reversed()); 96 } 97 } 98 } 99