Java BinaryOperator.apply方法代码示例

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
@Test
public void testIdentityConstraint() {
	// From javadoc of Collector interface:
	// The identity constraint says that for any partially accumulated result,
	// combining it with an empty result container must produce an equivalent result.
	// That is, for a partially accumulated result a that is the result of any series of 
	// accumulator and combiner invocations, a must be equivalent to combiner.apply(a, supplier.get()).
	
	StringCollector collector = new StringCollector(", ", "<!--", "-->");	
	Supplier<StringCombiner> supplier = collector.supplier();
	BiConsumer<StringCombiner, String> accumulator = collector.accumulator();
	BinaryOperator<StringCombiner> combiner = collector.combiner();
	Function<StringCombiner, String> finisher = collector.finisher();
	
	StringCombiner stringCombiner1 = supplier.get();
	accumulator.accept(stringCombiner1, "one");
	accumulator.accept(stringCombiner1, "two");
	String result1 = finisher.apply(stringCombiner1);
	
	StringCombiner stringCombiner2 = supplier.get();
	accumulator.accept(stringCombiner2, "one");
	accumulator.accept(stringCombiner2, "two");
	stringCombiner2 = combiner.apply(stringCombiner2, supplier.get());
	String result2 = finisher.apply(stringCombiner2);
	
	assertEquals(result1, result2);
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Constructs a {@code TerminalOp} that implements a mutable reduce on
 * {@code int} values.
 *
 * @param <R> The type of the result
 * @param supplier a factory to produce a new accumulator of the result type
 * @param accumulator a function to incorporate an int into an
 *        accumulator
 * @param combiner a function to combine an accumulator into another
 * @return A {@code ReduceOp} implementing the reduction
 */
public static <R> TerminalOp<Integer, R>
makeInt(Supplier<R> supplier,
        ObjIntConsumer<R> accumulator,
        BinaryOperator<R> combiner) {
    Objects.requireNonNull(supplier);
    Objects.requireNonNull(accumulator);
    Objects.requireNonNull(combiner);
    class ReducingSink extends Box<R>
            implements AccumulatingSink<Integer, R, ReducingSink>, Sink.OfInt {
        @Override
        public void begin(long size) {
            state = supplier.get();
        }

        @Override
        public void accept(int t) {
            accumulator.accept(state, t);
        }

        @Override
        public void combine(ReducingSink other) {
            state = combiner.apply(state, other.state);
        }
    }
    return new ReduceOp<Integer, R, ReducingSink>(StreamShape.INT_VALUE) {
        @Override
        public ReducingSink makeSink() {
            return new ReducingSink();
        }
    };
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Constructs a {@code TerminalOp} that implements a mutable reduce on
 * {@code double} values.
 *
 * @param <R> the type of the result
 * @param supplier a factory to produce a new accumulator of the result type
 * @param accumulator a function to incorporate an int into an
 *        accumulator
 * @param combiner a function to combine an accumulator into another
 * @return a {@code TerminalOp} implementing the reduction
 */
public static <R> TerminalOp<Double, R>
makeDouble(Supplier<R> supplier,
           ObjDoubleConsumer<R> accumulator,
           BinaryOperator<R> combiner) {
    Objects.requireNonNull(supplier);
    Objects.requireNonNull(accumulator);
    Objects.requireNonNull(combiner);
    class ReducingSink extends Box<R>
            implements AccumulatingSink<Double, R, ReducingSink>, Sink.OfDouble {
        @Override
        public void begin(long size) {
            state = supplier.get();
        }

        @Override
        public void accept(double t) {
            accumulator.accept(state, t);
        }

        @Override
        public void combine(ReducingSink other) {
            state = combiner.apply(state, other.state);
        }
    }
    return new ReduceOp<Double, R, ReducingSink>(StreamShape.DOUBLE_VALUE) {
        @Override
        public ReducingSink makeSink() {
            return new ReducingSink();
        }
    };
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Constructs a {@code TerminalOp} that implements a functional reduce on
 * reference values.
 *
 * @param <T> the type of the input elements
 * @param <U> the type of the result
 * @param seed the identity element for the reduction
 * @param reducer the accumulating function that incorporates an additional
 *        input element into the result
 * @param combiner the combining function that combines two intermediate
 *        results
 * @return a {@code TerminalOp} implementing the reduction
 */
public static <T, U> TerminalOp<T, U>
makeRef(U seed, BiFunction<U, ? super T, U> reducer, BinaryOperator<U> combiner) {
    Objects.requireNonNull(reducer);
    Objects.requireNonNull(combiner);
    class ReducingSink extends Box<U> implements AccumulatingSink<T, U, ReducingSink> {
        @Override
        public void begin(long size) {
            state = seed;
        }

        @Override
        public void accept(T t) {
            state = reducer.apply(state, t);
        }

        @Override
        public void combine(ReducingSink other) {
            state = combiner.apply(state, other.state);
        }
    }
    return new ReduceOp<T, U, ReducingSink>(StreamShape.REFERENCE) {
        @Override
        public ReducingSink makeSink() {
            return new ReducingSink();
        }
    };
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Constructs a {@code TerminalOp} that implements a mutable reduce on
 * {@code long} values.
 *
 * @param <R> the type of the result
 * @param supplier a factory to produce a new accumulator of the result type
 * @param accumulator a function to incorporate an int into an
 *        accumulator
 * @param combiner a function to combine an accumulator into another
 * @return a {@code TerminalOp} implementing the reduction
 */
public static <R> TerminalOp<Long, R>
makeLong(Supplier<R> supplier,
         ObjLongConsumer<R> accumulator,
         BinaryOperator<R> combiner) {
    Objects.requireNonNull(supplier);
    Objects.requireNonNull(accumulator);
    Objects.requireNonNull(combiner);
    class ReducingSink extends Box<R>
            implements AccumulatingSink<Long, R, ReducingSink>, Sink.OfLong {
        @Override
        public void begin(long size) {
            state = supplier.get();
        }

        @Override
        public void accept(long t) {
            accumulator.accept(state, t);
        }

        @Override
        public void combine(ReducingSink other) {
            state = combiner.apply(state, other.state);
        }
    }
    return new ReduceOp<Long, R, ReducingSink>(StreamShape.LONG_VALUE) {
        @Override
        public ReducingSink makeSink() {
            return new ReducingSink();
        }
    };
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Constructs a {@code TerminalOp} that implements a mutable reduce on
 * reference values.
 *
 * @param <T> the type of the input elements
 * @param <I> the type of the intermediate reduction result
 * @param collector a {@code Collector} defining the reduction
 * @return a {@code ReduceOp} implementing the reduction
 */
public static <T, I> TerminalOp<T, I>
makeRef(Collector<? super T, I, ?> collector) {
    Supplier<I> supplier = Objects.requireNonNull(collector).supplier();
    BiConsumer<I, ? super T> accumulator = collector.accumulator();
    BinaryOperator<I> combiner = collector.combiner();
    class ReducingSink extends Box<I>
            implements AccumulatingSink<T, I, ReducingSink> {
        @Override
        public void begin(long size) {
            state = supplier.get();
        }

        @Override
        public void accept(T t) {
            accumulator.accept(state, t);
        }

        @Override
        public void combine(ReducingSink other) {
            state = combiner.apply(state, other.state);
        }
    }
    return new ReduceOp<T, I, ReducingSink>(StreamShape.REFERENCE) {
        @Override
        public ReducingSink makeSink() {
            return new ReducingSink();
        }

        @Override
        public int getOpFlags() {
            return collector.characteristics().contains(Collector.Characteristics.UNORDERED)
                   ? StreamOpFlag.NOT_ORDERED
                   : 0;
        }
    };
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Constructs a {@code TerminalOp} that implements a functional reduce on
 * reference values producing an optional reference result.
 *
 * @param <T> The type of the input elements, and the type of the result
 * @param operator The reducing function
 * @return A {@code TerminalOp} implementing the reduction
 */
public static <T> TerminalOp<T, Optional<T>>
makeRef(BinaryOperator<T> operator) {
    Objects.requireNonNull(operator);
    class ReducingSink
            implements AccumulatingSink<T, Optional<T>, ReducingSink> {
        private boolean empty;
        private T state;

        public void begin(long size) {
            empty = true;
            state = null;
        }

        @Override
        public void accept(T t) {
            if (empty) {
                empty = false;
                state = t;
            } else {
                state = operator.apply(state, t);
            }
        }

        @Override
        public Optional<T> get() {
            return empty ? Optional.empty() : Optional.of(state);
        }

        @Override
        public void combine(ReducingSink other) {
            if (!other.empty)
                accept(other.state);
        }
    }
    return new ReduceOp<T, Optional<T>, ReducingSink>(StreamShape.REFERENCE) {
        @Override
        public ReducingSink makeSink() {
            return new ReducingSink();
        }
    };
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Atomically updates the current value with the results of
 * applying the given function to the current and given values,
 * returning the previous value. The function should be
 * side-effect-free, since it may be re-applied when attempted
 * updates fail due to contention among threads.  The function
 * is applied with the current value as its first argument,
 * and the given update as the second argument.
 *
 * @param x the update value
 * @param accumulatorFunction a side-effect-free function of two arguments
 * @return the previous value
 * @since 1.8
 */
public final V getAndAccumulate(V x,
                                BinaryOperator<V> accumulatorFunction) {
    V prev, next;
    do {
        prev = get();
        next = accumulatorFunction.apply(prev, x);
    } while (!compareAndSet(prev, next));
    return prev;
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Atomically updates the current value with the results of
 * applying the given function to the current and given values,
 * returning the updated value. The function should be
 * side-effect-free, since it may be re-applied when attempted
 * updates fail due to contention among threads.  The function
 * is applied with the current value as its first argument,
 * and the given update as the second argument.
 *
 * @param x the update value
 * @param accumulatorFunction a side-effect-free function of two arguments
 * @return the updated value
 * @since 1.8
 */
public final V accumulateAndGet(V x,
                                BinaryOperator<V> accumulatorFunction) {
    V prev, next;
    do {
        prev = get();
        next = accumulatorFunction.apply(prev, x);
    } while (!compareAndSet(prev, next));
    return next;
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Returns a {@code Collector} which performs a reduction of its
 * input elements under a specified mapping function and
 * {@code BinaryOperator}. This is a generalization of
 * {@link #reducing(Object, BinaryOperator)} which allows a transformation
 * of the elements before reduction.
 *
 * @apiNote
 * The {@code reducing()} collectors are most useful when used in a
 * multi-level reduction, downstream of {@code groupingBy} or
 * {@code partitioningBy}.  To perform a simple map-reduce on a stream,
 * use {@link Stream#map(Function)} and {@link Stream#reduce(Object, BinaryOperator)}
 * instead.
 *
 * <p>For example, given a stream of {@code Person}, to calculate the longest
 * last name of residents in each city:
 * <pre>{@code
 *     Comparator<String> byLength = Comparator.comparing(String::length);
 *     Map<City, String> longestLastNameByCity
 *         = people.stream().collect(groupingBy(Person::getCity,
 *                                              reducing(Person::getLastName, BinaryOperator.maxBy(byLength))));
 * }</pre>
 *
 * @param <T> the type of the input elements
 * @param <U> the type of the mapped values
 * @param identity the identity value for the reduction (also, the value
 *                 that is returned when there are no input elements)
 * @param mapper a mapping function to apply to each input value
 * @param op a {@code BinaryOperator<U>} used to reduce the mapped values
 * @return a {@code Collector} implementing the map-reduce operation
 *
 * @see #reducing(Object, BinaryOperator)
 * @see #reducing(BinaryOperator)
 */
public static <T, U>
Collector<T, ?, U> reducing(U identity,
                            Function<? super T, ? extends U> mapper,
                            BinaryOperator<U> op) {
    return new CollectorImpl<>(
            boxSupplier(identity),
            (a, t) -> { a[0] = op.apply(a[0], mapper.apply(t)); },
            (a, b) -> { a[0] = op.apply(a[0], b[0]); return a; },
            a -> a[0], CH_NOID);
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Atomically updates the element at index {@code i} with the
 * results of applying the given function to the current and
 * given values, returning the updated value. The function should
 * be side-effect-free, since it may be re-applied when attempted
 * updates fail due to contention among threads.  The function is
 * applied with the current value at index {@code i} as its first
 * argument, and the given update as the second argument.
 *
 * @param i the index
 * @param x the update value
 * @param accumulatorFunction a side-effect-free function of two arguments
 * @return the updated value
 * @since 1.8
 */
public final E accumulateAndGet(int i, E x,
                                BinaryOperator<E> accumulatorFunction) {
    long offset = checkedByteOffset(i);
    E prev, next;
    do {
        prev = getRaw(offset);
        next = accumulatorFunction.apply(prev, x);
    } while (!compareAndSetRaw(offset, prev, next));
    return next;
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Atomically updates (with memory effects as specified by {@link
 * VarHandle#compareAndSet}) the field of the given object managed
 * by this updater with the results of applying the given function
 * to the current and given values, returning the updated value.
 * The function should be side-effect-free, since it may be
 * re-applied when attempted updates fail due to contention among
 * threads.  The function is applied with the current value as its
 * first argument, and the given update as the second argument.
 *
 * @param obj An object whose field to get and set
 * @param x the update value
 * @param accumulatorFunction a side-effect-free function of two arguments
 * @return the updated value
 * @since 1.8
 */
public final V accumulateAndGet(T obj, V x,
                                BinaryOperator<V> accumulatorFunction) {
    V prev, next;
    do {
        prev = get(obj);
        next = accumulatorFunction.apply(prev, x);
    } while (!compareAndSet(obj, prev, next));
    return next;
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Atomically updates the field of the given object managed by this
 * updater with the results of applying the given function to the
 * current and given values, returning the updated value. The
 * function should be side-effect-free, since it may be re-applied
 * when attempted updates fail due to contention among threads.  The
 * function is applied with the current value as its first argument,
 * and the given update as the second argument.
 *
 * @param obj An object whose field to get and set
 * @param x the update value
 * @param accumulatorFunction a side-effect-free function of two arguments
 * @return the updated value
 * @since 1.8
 */
public final V accumulateAndGet(T obj, V x,
                                BinaryOperator<V> accumulatorFunction) {
    V prev, next;
    do {
        prev = get(obj);
        next = accumulatorFunction.apply(prev, x);
    } while (!compareAndSet(obj, prev, next));
    return next;
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Atomically updates the element at index {@code i} with the
 * results of applying the given function to the current and
 * given values, returning the previous value. The function should
 * be side-effect-free, since it may be re-applied when attempted
 * updates fail due to contention among threads.  The function is
 * applied with the current value at index {@code i} as its first
 * argument, and the given update as the second argument.
 *
 * @param i the index
 * @param x the update value
 * @param accumulatorFunction a side-effect-free function of two arguments
 * @return the previous value
 * @since 1.8
 */
public final E getAndAccumulate(int i, E x,
                                BinaryOperator<E> accumulatorFunction) {
    long offset = checkedByteOffset(i);
    E prev, next;
    do {
        prev = getRaw(offset);
        next = accumulatorFunction.apply(prev, x);
    } while (!compareAndSetRaw(offset, prev, next));
    return prev;
}
 

import java.util.function.BinaryOperator; //导入方法依赖的package包/类
/**
 * Atomically updates (with memory effects as specified by {@link
 * VarHandle#compareAndSet}) the current value with the results of
 * applying the given function to the current and given values,
 * returning the previous value. The function should be
 * side-effect-free, since it may be re-applied when attempted
 * updates fail due to contention among threads.  The function is
 * applied with the current value as its first argument, and the
 * given update as the second argument.
 *
 * @param x the update value
 * @param accumulatorFunction a side-effect-free function of two arguments
 * @return the previous value
 * @since 1.8
 */
public final V getAndAccumulate(V x,
                                BinaryOperator<V> accumulatorFunction) {
    V prev = get(), next = null;
    for (boolean haveNext = false;;) {
        if (!haveNext)
            next = accumulatorFunction.apply(prev, x);
        if (weakCompareAndSetVolatile(prev, next))
            return prev;
        haveNext = (prev == (prev = get()));
    }
}