/*
* Javolution - Java(TM) Solution for Real-Time and Embedded Systems
* Copyright (C) 2012 - Javolution (http://javolution.org/)
* All rights reserved.
*
* Permission to use, copy, modify, and distribute this software is
* freely granted, provided that this notice is preserved.
*/
package javolution.util.function;
import static javolution.lang.Realtime.Limit.LINEAR;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicReference;
import javolution.lang.Parallelizable;
import javolution.lang.Realtime;
import javolution.util.FastCollection;
/**
* <p> A set of useful {@link Reducer reducers} of collection elements.</p>
*
* @author <a href="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a>
* @version 6.0, July 21, 2013
* @see FastCollection#reduce(Reducer)
*/
public class Reducers {
// Utility class, no default constructor.
private Reducers() {}
/**
* Returns any non-null element of the specified type.
* This reducer stops iterating as soon as an element with the matching
* type is found.
*/
@Parallelizable
@Realtime(limit = LINEAR)
public static <E> Reducer<E> any(Class<? extends E> type) {
return new AnyReducer<E>(type);
}
private static class AnyReducer<E> implements Reducer<E> {
private final Class<? extends E> type;
private volatile E found;
public AnyReducer(Class<? extends E> type) {
this.type = type;
}
@Override
public void accept(Collection<E> param) {
Iterator<E> it = param.iterator();
while (it.hasNext() && (found == null)) {
E e = it.next();
if (type.isInstance(e)) {
found = e;
break;
}
}
}
@Override
public E get() {
return found;
}
}
/**
* Returns the greatest element of a collection according to the
* specified comparator (returns {@code null} if the collection is empty).
*/
@Parallelizable(mutexFree = true, comment = "Internal use of AtomicReference")
@Realtime(limit = LINEAR)
public static <E> Reducer<E> max(Comparator<? super E> comparator) {
return new MaxReducer<E>(comparator);
}
private static class MaxReducer<E> implements Reducer<E> {
private final Comparator<? super E> cmp;
private final AtomicReference<E> max = new AtomicReference<E>(null);
public MaxReducer(Comparator<? super E> cmp) {
this.cmp = cmp;
}
@Override
public void accept(Collection<E> param) {
Iterator<E> it = param.iterator();
while (it.hasNext()) {
E e = it.next();
E read = max.get();
while ((read == null) || (cmp.compare(e, read) > 0)) {
if (max.compareAndSet(read, e)) break;
read = max.get();
}
}
}
@Override
public E get() {
return max.get();
}
}
/**
* Returns the smallest element of a collection according to the collection
* comparator (returns {@code null} if the collection is empty).
*/
@Parallelizable(mutexFree = true, comment = "Internal use of AtomicReference")
@Realtime(limit = LINEAR)
public static <E> Reducer<E> min(Comparator<? super E> comparator) {
return new MinReducer<E>(comparator);
}
private static class MinReducer<E> implements Reducer<E> {
private final Comparator<? super E> cmp;
private final AtomicReference<E> min = new AtomicReference<E>(null);
public MinReducer(Comparator<? super E> cmp) {
this.cmp = cmp;
}
@Override
public void accept(Collection<E> param) {
Iterator<E> it = param.iterator();
while (it.hasNext()) {
E e = it.next();
E read = min.get();
while ((read == null) || (cmp.compare(e, read) < 0)) {
if (min.compareAndSet(read, e)) break;
read = min.get();
}
}
}
@Override
public E get() {
return min.get();
}
}
/**
* Conditional 'and' operator (returns {@code true} if the collection is
* empty). This operator stops iterating as soon as a {@code false} value
* is found.
*/
@Parallelizable
@Realtime(limit = LINEAR)
public static Reducer<Boolean> and() {
return new AndReducer();
}
private static class AndReducer implements Reducer<Boolean> {
volatile boolean result = true;
@Override
public void accept(Collection<Boolean> param) {
Iterator<Boolean> it = param.iterator();
while (result && it.hasNext()) {
if (!it.next()) result = false;
}
}
@Override
public Boolean get() {
return result;
}
}
/**
* Conditional 'or' operator (returns {@code false} if the collection is
* empty). This operator stops iterating as soon as a {@code true} value
* is found.
*/
@Parallelizable
@Realtime(limit = LINEAR)
public static Reducer<Boolean> or() {
return new OrReducer();
}
private static class OrReducer implements Reducer<Boolean> {
volatile boolean result = false;
@Override
public void accept(Collection<Boolean> param) {
Iterator<Boolean> it = param.iterator();
while (!result && it.hasNext()) {
if (!it.next()) result = true;
}
}
@Override
public Boolean get() {
return result;
}
}
/**
* Returns the sum of the specified integers value (returns {@code 0}
* if the collection is empty).
*/
@Parallelizable(comment = "Internal use of AtomicInteger")
@Realtime(limit = LINEAR)
public static Reducer<Integer> sum() {
return new SumReducer();
}
private static class SumReducer implements Reducer<Integer> {
private final AtomicInteger sum = new AtomicInteger(0);
@Override
public void accept(Collection<Integer> param) {
Iterator<Integer> it = param.iterator();
while (it.hasNext()) {
sum.getAndAdd(it.next().intValue());
}
}
@Override
public Integer get() {
return sum.get();
}
}
}