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Drozdov Igor lesson 4 #177

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e01d95c
ReachIterable and Traversable
eye-dee Jul 6, 2017
6366cdb
fix
eye-dee Jul 17, 2017
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194 changes: 187 additions & 7 deletions src/test/java/lambda/part3/exercise/Mapping.java
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Original file line number Diff line number Diff line change
Expand Up @@ -5,16 +5,14 @@
import data.Person;
import org.junit.Test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.function.BiConsumer;
import java.util.*;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

public class Mapping {

Expand Down Expand Up @@ -81,7 +79,7 @@ public void mapping() {
.map(TODO) // add 1 year to experience duration .map(e -> e.withJobHistory(addOneYear(e.getJobHistory())))
.map(TODO) // replace qa with QA
* */
.getList();
.getList();

final List<Employee> expectedResult =
Arrays.asList(
Expand Down Expand Up @@ -165,7 +163,189 @@ public <R2> LazyFlatMapHelper<T, R2> flatMap(Function<R, List<R2>> f) {
}
}

interface ReachIterable<T> {
boolean tryGet(Consumer<T> consumer);

static<T> ReachIterable<T> from(List<T> list) {
final Iterator<T> iterator = list.iterator();
return new ReachIterable<T>() {
@Override
public boolean tryGet(Consumer<T> consumer) {
if (iterator.hasNext()) {
consumer.accept(iterator.next());
return true;
} else {
return false;
}
}
};
}

default List<T> force() {
final List<T> result = new ArrayList<>();
while (tryGet(result::add));
return result;
}

default ReachIterable<T> filter(Predicate<T> predicate) {
final ReachIterable<T> self = this;
return new ReachIterable<T>() {
@Override
public boolean tryGet(Consumer<T> consumer) {
return self.tryGet(t -> {
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@senia-psm senia-psm Jul 17, 2017

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Incorrect. You should either return false or return true and call consumer.

if (predicate.test(t)) {
consumer.accept(t);
}
});
}
};
}

default <R> ReachIterable<R> map(final Function<T, R> function) {
final ReachIterable<T> self = this;
return new ReachIterable<R>() {
@Override
public boolean tryGet(final Consumer<R> consumer) {
return self.tryGet(t -> consumer.accept(function.apply(t)));
}
};
}

default <R> ReachIterable<R> flatMap(Function<T, ReachIterable<R>> function) {
final ReachIterable<T> self = this;
return new ReachIterable<R>() {
private ReachIterable<R> reachIterable;
@Override
public boolean tryGet(final Consumer<R> consumer) {
boolean res = self.tryGet(t -> reachIterable = function.apply(t));
while (reachIterable.tryGet(consumer));
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@senia-psm senia-psm Jul 17, 2017

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Incorrect. You should call consumer only once.

return res;
}
};
}

default boolean anyMatch(Predicate<T> p) {
return firstMatch(p).isPresent();
}

default boolean allMatch(Predicate<T> predicate) {
return !anyMatch(predicate.negate());
}

default boolean noneMatch(Predicate<T> predicate) {
return !anyMatch(predicate);
}

default Optional<T> firstMatch(Predicate<T> predicate) {
final Object[] objects = new Object[1];
while (tryGet(t -> {
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Incorrect. firstMatch should be able to return value in case of infinite stream.

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@eye-dee eye-dee Jul 17, 2017

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It will return value, when test return true.

if (predicate.test(t)) {
objects[0] = t;
}
})) {
if (objects[0] != null) {
return Optional.of((T)objects[0]);
}
}
return Optional.empty();
}
}

@Test
public void reachIterable() {
final List<Integer> integers = ReachIterable.from(Arrays.asList("1", "2", "3", "4", "5"))
.map(Integer::valueOf)
.filter(i -> i % 2 == 0)
.force();

assertEquals(integers, Arrays.asList(2,4));

final Optional<String> stringOptional = ReachIterable.from(Arrays.asList("1", "2", "3", "4", "5"))
.firstMatch(s -> s.equals("3"));

assertEquals(stringOptional, Optional.of("3"));

assertEquals(ReachIterable.from(Collections.singletonList("1")).firstMatch(s -> s.length() == 5), Optional.empty());

assertTrue(ReachIterable.from(Arrays.asList("1", "2", "3"))
.noneMatch(s -> s.length() == 3));

assertTrue(ReachIterable.from(Arrays.asList("1", "2", "3"))
.allMatch(s -> s.length() == 1));


final List<Integer> integers2 = ReachIterable.from(Arrays.asList(new String[][]{{"1", "2"}, {"3", "4"}, {"5", "6"}, {}}))
.flatMap(strings -> ReachIterable.from(Arrays.stream(strings).collect(Collectors.toList())))
.map(Integer::valueOf)
.filter(i -> i % 2 == 0)
.force();

assertEquals(integers2, Arrays.asList(2,4,6));
}

interface Traversable<T> {
void forEach(Consumer<T> consumer);

default <R> Traversable<R> flatMap(Function<T, Traversable<R>> function) {
final Traversable<T> self = this;
return new Traversable<R>() {
@Override
public void forEach(Consumer<R> consumer) {
self.forEach(t -> function.apply(t).forEach(consumer));
}
};
}

default Traversable<T> filter(Predicate<T> predicate) {
final Traversable<T> self = this;
return new Traversable<T>() {
@Override
public void forEach(Consumer<T> consumer) {
self.forEach(t -> {
if (predicate.test(t)) {
consumer.accept(t);
}
});
}
};
}

default <R> Traversable<R> map(Function<T,R> function) {
final Traversable<T> self = this;
return new Traversable<R>() {
@Override
public void forEach(Consumer<R> consumer) {
self.forEach(t -> consumer.accept(function.apply(t)));
}
};
}

default List<T> toList() {
final List<T> result = new ArrayList<>();
forEach(result::add);
return result;
}

static <T> Traversable<T> from(List<T> list) {
return new Traversable<T>() {
@Override
public void forEach(Consumer<T> consumer) {
list.forEach(consumer);
}
};
}
}

@Test
public void traversable() {
final List<Integer> integers = Traversable.from(Arrays.asList(new String[][]{{"1", "2"}, {"3", "4"}, {"5", "6"}}))
.flatMap(strings -> Traversable.from(Arrays.stream(strings).collect(Collectors.toList())))
.map(Integer::valueOf)
.filter(i -> i % 2 == 0)
.toList();

assertEquals(integers, Arrays.asList(2,4,6));
}

@Test
public void lazy_mapping() {
Expand Down Expand Up @@ -198,7 +378,7 @@ public void lazy_mapping() {
.map(TODO) // add 1 year to experience duration
.map(TODO) // replace qa with QA
* */
.force();
.force();

final List<Employee> expectedResult =
Arrays.asList(
Expand Down