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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.collections;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Random;
import java.util.Set;
import java.util.Spliterator;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import static java.util.stream.Collectors.toList;
/**
* Abstract, immutable list for subclassing with concrete types and domain specific filters.
*
* @author jonmv
*/
public abstract class AbstractFilteringList<Type, ListType extends AbstractFilteringList<Type, ListType>> implements Iterable<Type> {
private final List<Type> items;
private final boolean negate;
private final BiFunction<List<Type>, Boolean, ListType> constructor;
// Subclass constructor:
// private SomeFilteringList(Collection<? extends SomeType> items, boolean negate) {
// super(items, negate, SomeFilteringList::new);
// }
protected AbstractFilteringList(Collection<? extends Type> items, boolean negate, BiFunction<List<Type>, Boolean, ListType> constructor) {
this.items = List.copyOf(items);
this.negate = negate;
this.constructor = constructor;
}
/** Negates the next filter operation. All other operations which return a new list reset this modifier. */
public final ListType not() {
return constructor.apply(items, ! negate);
}
/** Returns a new list which is the result of filtering with the -- possibly negated -- condition. */
public final ListType matching(Predicate<Type> condition) {
return constructor.apply(items.stream().filter(negate ? condition.negate() : condition).toList(), false);
}
/** Returns the first n items in this list, or everything except those if negated. */
public ListType first(int n) {
n = Math.min(n, items.size());
return constructor.apply(items.subList(negate ? n : 0, negate ? items.size() : n), false);
}
/** Returns the first item in this list, or empty if there are none. */
public Optional<Type> first() {
return items.stream().findFirst();
}
/** Returns the subset of items in this which are (not) present in the other list. */
public ListType in(ListType others) {
return matching(new HashSet<>(others.asList())::contains);
}
/** Returns the concatenation of the two lists. */
public ListType and(ListType others) {
return constructor.apply(Stream.concat(items.stream(), others.asList().stream()).toList(), false);
}
/** Returns the items in this as an immutable list. */
public final List<Type> asList() { return items; }
/** Returns the items in this as a set. */
public final Set<Type> asSet() { return new HashSet<>(items); }
/** Returns the items in this as an immutable list after mapping with the given function. */
public final <OtherType> List<OtherType> mapToList(Function<Type, OtherType> mapper) {
return items.stream().map(mapper).toList();
}
/** Returns the items sorted by the given comparator. */
public final ListType sortedBy(Comparator<? super Type> comparator) {
return constructor.apply(items.stream().sorted(comparator).toList(), false);
}
/** Returns the items grouped by the given classifier. */
public final <OtherType> Map<OtherType, ListType> groupingBy(Function<Type, OtherType> classifier) {
return items.stream().collect(Collectors.groupingBy(classifier,
LinkedHashMap::new,
Collectors.collectingAndThen(toList(),
(list) -> constructor.apply(list, false))));
}
public final boolean isEmpty() { return items.isEmpty(); }
public final int size() { return items.size(); }
@Override
public Iterator<Type> iterator() {
return items.iterator();
}
@Override
public Spliterator<Type> spliterator() {
return items.spliterator();
}
/** Returns the items in this shuffled using random as source of randomness */
public final ListType shuffle(Random random) {
ArrayList<Type> shuffled = new ArrayList<>(items);
Collections.shuffle(shuffled, random);
return constructor.apply(shuffled, false);
}
}
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