Functional Programming

Question 1

What types of variables can lambda expressions use?

Answer 1

static variables
instance variables
effectively final variables in methods (effectively final meaning they are only ever assigned one value and never altered)

Question 2

Functional Interface

Supplier

1) # of Parameters?
2) Return Type?
3) Single Abstract Method It Contains?

Answer 2

1) 0
2) T
3) get

Question 3

Functional Interface

Consumer

1) # of Parameters?
2) Return Type?
3) Single Abstract Method It Contains?

Answer 3

1) 1 (T)
2) void
3) accept

Question 4

Functional Interface

BiConsumer

1) # of Parameters?
2) Return Type?
3) Single Abstract Method It Contains?

Answer 4

1) 2 (T, U)
2) void
3) accept

Question 5

Functional Interface

Predicate

1) # of Parameters?
2) Return Type?
3) Single Abstract Method It Contains?

Answer 5

1) 1 (T)
2) boolean
3) test

Question 6

Functional Interface

BiPredicate

1) # of Parameters?
2) Return Type?
3) Single Abstract Method It Contains?

Answer 6

1) 2 (T, U)
2) boolean
3) test

Question 7

Functional Interface

Function

1) # of Parameters?
2) Return Type?
3) Single Abstract Method It Contains?

Answer 7

1) 1 (T)
2) R
3) apply

Question 8

Functional Interface

BiFunction

1) # of Parameters?
2) Return Type?
3) Single Abstract Method It Contains?

Answer 8

1) 2 (T, U)
2) R
3) apply

Question 9

Functional Interface

UnaryOperator

1) # of Parameters?
2) Return Type?
3) Single Abstract Method It Contains?

Answer 9

1) 1 (T)
2) T`
3) apply

Question 10

Functional Interface

BinaryOperator

1) # of Parameters?
2) Return Type?
3) Single Abstract Method It Contains?

Answer 10

1) 2 (T, T)
2) T`
3) apply

Question 11

When do you use the Supplier functional interface?

Answer 11

When you want to generate or supply values without taking any input.

Think of it as creating something to supply

Question 12

When do you use the Consumer or BiConsumer functional interface?

Answer 12

When you want to do something with a parameter (or two if BiConsumer) but not return anything.

Think of it as consuming the parameters

Question 13

When do you use the Predicate or BiPredicate functional interface?

Answer 13

When filtering or matching.

It checks for a certain condition and returns true or false.

Question 14

When do you use the Function or BiFunction functional interface?

Answer 14

When turning parameters into a value of a potentially different type and returning it.

Use the parameters to calculate/determine a result

Question 15

When do you use the UnaryOperator or BinaryOperator functional interface?

Answer 15

When you want to transform a value (or two) into another value of the same type.

UnaryOperator extends Function

BinaryOperator extends BiFunction

Question 16

Optional

Answer 16

A container object which may or may not contain a non-null value

Question 17

How to represent an empty Optional object?

Answer 17

Optional.empty()

Question 18

How to represent an Optional object with a value of 30?

Answer 18

Optional.of(30)

Question 19

Optional.ofNullable(val)

Answer 19

Returns an Optional.empty() if val is null, or Optional.of(val) if val is non-null

Question 20

Optional instance method

get()

Answer 20

When the Optional is empty, throws an exception

When the Optional contains a value, returns the value

Question 21

Optional instance method

ifPresent(Consumer c)

Answer 21

When the Optional is empty, does nothing

When the Optional contains a value, calls Consumer c with the value

Question 22

Optional instance method

isPresent()

Answer 22

When the Optional is empty, returns false

When the Optional contains a value, returns true

Question 23

Optional instance method

orElse(T other)

Answer 23

When the Optional is empty, returns other

When the Optional contains a value, returns the value

Question 24

Optional instance method

orElseGet(Supplier s)

Answer 24

When the Optional is empty, returns result of calling Supplier s

When the Optional contains a value, returns the value

Question 25

Optional instance method orElseThrow(Supplier s)

Answer 25

When the Optional is empty, throws the exception created by calling Supplier s When the Optional contains a value, returns the value

Question 26

Stream

Answer 26

A sequence of data

Question 27

Stream Pipeline

Answer 27

The operations that run on a stream to produce a result It has a source which starts the stream, intermediate operations that produce a chain of streams, and the final operation that produces the result, known as the terminal operation.

Question 28

Stream package

Answer 28

java.util.stream

Question 29

How to create an empty Stream

Answer 29

Stream empty = Stream.empty();

Question 30

How to create a Stream with elements

Answer 30

Stream.of(T... t) Can be one value, comma separated values, or an array

Question 31

How to create a Stream from a List

Answer 31

list.stream() or list.parallelStream(); // Allows the stream to process elements in parallel

Question 32

What does the following code do? Stream.generate(Math::random)

Answer 32

Generates infinite random numbers

Question 33

What does the following code do? Stream.iterate(1, n -> n + 2)

Answer 33

Generates infinite odd numbers It starts with 1, then continues infinitely using the previous result as n in the lambda

Question 34

What is a reduction?

Answer 34

A special type of terminal operation where all of the contents of the stream are combined into a single primitive or Object.

Question 35

Terminal Operation count()

Answer 35

Determines the number of elements in a finite stream. Returns a long

Question 36

Terminal Operations min() and max()

Answer 36

Allow you to pass a custom comparator and find the smallest or largest value in a finite stream according to that sort order. ``` Optional min( super T> comparator) Optional max( super T> comparator) ```

Question 37

Terminal Operations findAny() and findFirst()

Answer 37

findAny() will return any element in the stream so long as it is not empty findFirst() will return the first element in the stream so long as it is not empty Works with infinite streams! ``` Optional findAny() Optional findFirst() ```

Question 38

Terminal Operations anyMatch(), allMatch(), noneMatch()

Answer 38

anyMatch will find out whether at least one of the elements in the stream matches a given predicate. allMatch will check every element in the stream and find out if it matches the predicate. noneMatch will find if no elements in the stream match the specified predicate. boolean anyMatch(Predicate super T> predicate) boolean allMatch(Predicate super T> predicate) boolean noneMatch(Predicate super T> predicate)

Question 39

Terminal Operation forEach()

Answer 39

forEach will perform an action for each element in the stream. It is a simplified inline way to write a for loop. void forEach(Consumer super T> action)

Question 40

Terminal Operation reduce()

Answer 40

reduce uses a BinaryOperator to combine the elements of the stream into a single object. Stream stream = Stream.of(3, 5, 6); System.out.println(stream.reduce(1, (a, b) -> a*b)); //90 ``` T reduce(T identity, BinaryOperator accumulator) Optional reduce(BinaryOperator accumulator) U reduce(U identity, BiFunction accumulator, BinaryOperator combiner) ```

Question 41

Terminal Operation collect()

Answer 41

collect will convert the stream into some other container Stream stream = Stream.of("w", "o", "l", "f"); StringBuilder word = stream.collect(StringBuilder::new, StringBuilder::append, StringBuilder:append) In this example, StringBuilder::new creates the object we will be adding elements of the stream to, the first StringBuilder::append tells it how to handle adding one element, and the second StringBuilder::append tells it how to handle combining two containers together (however it chooses to do that in the process) ``` R collect(Supplier supplier, BiConsumer accumulator, BiConsumer combiner) R collect(Collector super T, A,R> collector) ``` You can also use a predefined Collector such as this: Stream stream = Stream.of("w", "o", "l", "f"); Set set = stream.collect(Collectors.toSet());

Question 42

Intermediate Operation filter()

Answer 42

Returns a Stream with elements that match a given expression Stream filter(Predicate super T> predicate) Stream s = Stream.of("monkey", "gorilla", "bonobo"); s.filter(x -> x.startsWith("m")).forEach(System.out::print); // monkey

Question 43

Intermediate Operation distinct()

Answer 43

Returns a stream with duplicate values removed Stream distinct() Stream s = Stream.of("duck", "duck", "duck", "goose"); s.distinct().forEach(System.out::print); // duckgoose

Question 44

Intermediate Operations limit() and skip()

Answer 44

limit(n) specifies the max size of the stream is n skip(n) will skip to the nth element in the stream ``` Stream limit(int maxSize) Stream skip(int n) ``` Stream s = Stream.iterate(1, n -> n + 1); s.skip(5).limit(2).forEach(System.out::print); // 67

Question 45

Intermediate Operation map()

Answer 45

map will transform the elements elements in a stream using the provided Function Stream map(Function super T, ? extends R> mapper) Stream s = Stream.of("monkey", "gorilla", "bonobo"); s.map(String::length).forEach(System.out::print); // 676

Question 46

Intermediate Operation flatMap()

Answer 46

Takes each element in the stream and makes any elements it contains top-level elements in a single stream. This is helpful when you want to remove empty elements from a stream or you want to combine a stream of lists. List zero = Arrays.asList(); List one = Arrays.asList("Bonobo"); List two = Arrays.asList("Mama Gorilla", "Baby Gorilla"); Stream> animals = Stream.of(zero, one, two); animals.flatMap(l -> l.stream()).forEach(System.out::println);

Question 47

Intermediate Operation sorted()

Answer 47

Returns a stream with the elements sorted ``` Stream sorted() Stream sorted(Comparator super T> comparator) ```

Question 48

Intermediate Operation peek()

Answer 48

Allows you to perform an operation on the current element of the stream Stream peek(Consumer super T> action) Stream s = Stream.of("monkey", "gorilla", "bonobo"); s.peek(System.out::println);

Question 49

What is the result of this code? ``` Stream.generate(() -> "Elsa") .filter(n -> n.length() == 4) .sorted() .limit(2) .forEach(System.out::println); ```

Answer 49

It hangs until you kill it. Sorted will wait to sort until filter is done passing it stuff, so it never reaches the limit(2)

Question 50

What is the result of this code? ``` Stream.generate(() -> "Elsa") .filter(n -> n.length() == 4) .limit(2) .sorted() .forEach(System.out::println); ```

Answer 50

Elsa Elsa When filter passes 2 elements through to sorted(), limit(2) tells the code to move on and do the sort.

Question 51

What is the result of this code? Stream infinite = Stream.iterate(1, x -> x + 1); infinite.filter(x -> x % 2 == 1) .peek(System.out::print) .limit(5) .forEach(System.out::print);

Answer 51

1133557799 The elements of the stream get passed through all the way down the pipeline before the next one

Question 52

IntStream

Answer 52

A stream that contains primitives. Can be used for int, short, byte or char

Question 53

LongStream

Answer 53

A stream that contains primitives. Can be used for long

Question 54

DoubleStream

Answer 54

A stream that contains primitives. Can be used for double or float

Question 55

How to get the average of the numbers in this stream? IntStream intStream = IntStream.of(1, 2, 3);

Answer 55

intStream.average() Returns an OptionalDouble

Question 56

How to create an IntStream with the numbers in the range 1-5?

Answer 56

IntStream range = IntStream.range(1,6) IntStream range = IntStream.rangeClosed(1,5)

Question 57

How to get the sum of the elements in this stream? IntStream intStream = IntStream.of(1, 2, 3);

Answer 57

intStream.sum() Returns an int

Question 58

How to find the largest and smallest element in this stream? IntStream intStream = IntStream.of(1, 2, 3);

Answer 58

intStream.max() intStream.min() Returns an OptionalInt

Question 59

How to retrieve the value of the following OptionalInt? OptionalInt optional;

Answer 59

optional.getAsInt() If no element present, throws NoSuchElementException

Question 60

How to get info on an IntStream that includes the minimum, maximum, average, size, and the number of values in the stream.

Answer 60

IntSummaryStatistics stats = intStream.summaryStatistics(); ``` getAverage() getCount() getMax() getMin() getSum() ```

Question 61

BooleanSupplier

Answer 61

Functional interface for boolean boolean getAsBoolean()

Question 62

What is the output of the following code? Stream ohMy = Stream.of("lions", "tigers", "bears"); String result = ohMy.collect(Collectors.joining(", ")); System.out.println(result);

Answer 62

lions, tigers, bears

Question 63

What is the output of the following code? Stream ohMy = Stream.of("lion", "tigers", "bears"); Double result = ohMy.collect(Collectors.averagingInt(String::length)); System.out.println(result);

Answer 63

5.0 | a Double