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Comparators.java
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98 lines (88 loc) · 2.38 KB
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/*
* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util;
import java.io.Serializable;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.ToDoubleFunction;
import java.util.function.ToIntFunction;
import java.util.function.ToLongFunction;
/**
* Package private supporting class for {@link Comparator}.
*/
class Comparators {
private Comparators() {
throw new AssertionError("no instances");
}
/**
* Compares {@link Comparable} objects in natural order.
*
* @see Comparable
*/
enum NaturalOrderComparator implements Comparator<Comparable<Object>> {
INSTANCE;
@Override
public int compare(Comparable<Object> c1, Comparable<Object> c2) {
return c1.compareTo(c2);
}
@Override
public Comparator<Comparable<Object>> reversed() {
return Comparator.reverseOrder();
}
}
/**
* Null-friendly comparators
*/
final static class NullComparator<T> implements Comparator<T>, Serializable {
private static final long serialVersionUID = -7569533591570686392L;
private final boolean nullFirst;
// if null, non-null Ts are considered equal
private final Comparator<T> real;
@SuppressWarnings("unchecked")
NullComparator(boolean nullFirst, Comparator<? super T> real) {
this.nullFirst = nullFirst;
this.real = (Comparator<T>) real;
}
@Override
public int compare(T a, T b) {
if (a == null) {
return (b == null) ? 0 : (nullFirst ? -1 : 1);
} else if (b == null) {
return nullFirst ? 1: -1;
} else {
return (real == null) ? 0 : real.compare(a, b);
}
}
@Override
public Comparator<T> thenComparing(Comparator<? super T> other) {
Objects.requireNonNull(other);
return new NullComparator<>(nullFirst, real == null ? other : real.thenComparing(other));
}
@Override
public Comparator<T> reversed() {
return new NullComparator<>(!nullFirst, real == null ? null : real.reversed());
}
}
}