Value (Javaslang 2.0.0-RC2 API)

Type Parameters:

T - The type of the wrapped value.

All Superinterfaces:

Foldable<T>, Functor<T>, Iterable<T>, Monad<T>

All Known Subinterfaces:

Arbitrary<T>, Future<T>, Gen<T>, IndexedSeq<T>, Iterator<T>, Lazy<T>, LinearSeq<T>, List<T>, Map<K,V>, Match.MatchMonad<R>, Option<T>, Seq<T>, Set<T>, SortedMap<K,V>, SortedSet<T>, Stack<T>, Stream<T>, Traversable<T>, Tree<T>, Try<T>

All Known Implementing Classes:

Array, CharSeq, Either.LeftProjection, Either.RightProjection, Failure, HashMap, HashSet, Lazy.Defined, Lazy.Undefined, LinkedHashMap, LinkedHashSet, List.Cons, List.Nil, Match.MatchMonad.Otherwise, Match.MatchMonad.When.Then, None, Queue, Some, Stream.Cons, Stream.Empty, Success, Tree.Empty, Tree.Node, TreeMap, TreeSet, Vector
```
public interface Value<T>
extends Foldable<T>, Monad<T>
```
Functional programming is all about values and transformation of values using functions. The Value type reflects the values in a functional setting. It can be seen as the result of a partial function application. Hence the result may be undefined. If a value is undefined, we say it is empty.
How the empty state is interpreted depends on the context, i.e. it may be undefined, failed, not yet defined, etc.
Static methods:
- get(java.lang.Iterable)
Basic operations:
Equality checks:
- corresponds(java.lang.Iterable, BiPredicate)
- eq(Object)
Side-effects:
Tests:
- isSingletonType()
Since:

2.0.0

Author:

Daniel Dietrich

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method and Description
`default <U> boolean`	`corresponds(Iterable<U> that, java.util.function.BiPredicate<? super T,? super U> predicate)` Tests whether every element of this iterable relates to the corresponding element of another iterable by satisfying a test predicate.
`default boolean`	`eq(Object o)` A smoothing replacement for `equals`.
`boolean`	`equals(Object o)` Clarifies that values have a proper equals() method implemented.
`default boolean`	`exists(java.util.function.Predicate<? super T> predicate)` Checks, if an element exists such that the predicate holds.
`Value<T>`	`filter(java.util.function.Predicate<? super T> predicate)` Filters this `Monad` by testing a predicate.
`<U> Value<U>`	`flatMap(java.util.function.Function<? super T,? extends Iterable<? extends U>> mapper)` FlatMaps this value to a new value with different component type.
`default <U> U`	`foldLeft(U zero, java.util.function.BiFunction<? super U,? super T,? extends U> combine)` Folds this elements from the left, starting with `zero` and successively calling `combine`.
`default <U> U`	`foldRight(U zero, java.util.function.BiFunction<? super T,? super U,? extends U> combine)` Folds this elements from the right, starting with `zero` and successively calling `combine`.
`default boolean`	`forAll(java.util.function.Predicate<? super T> predicate)` Checks, if the given predicate holds for all elements.
`default void`	`forEach(java.util.function.Consumer<? super T> action)` Performs an action on each element.
`T`	`get()` Gets the underlying value or throws if no value is present.
`static <T> T`	`get(Iterable<? extends T> iterable)` Gets the first value of the given Iterable if exists, otherwise throws.
`default Option<T>`	`getOption()` Gets the underlying as Option.
`int`	`hashCode()` Clarifies that values have a proper hashCode() method implemented.
`default T`	`ifDefined(java.util.function.Supplier<? extends T> trueSupplier, java.util.function.Supplier<? extends T> falseSupplier)` A fluent if-expression for this value.
`default T`	`ifDefined(T trueVal, T falseVal)` A fluent if-expression for this value.
`default T`	`ifEmpty(java.util.function.Supplier<? extends T> trueSupplier, java.util.function.Supplier<? extends T> falseSupplier)` A fluent if-expression for this value.
`default T`	`ifEmpty(T trueVal, T falseVal)` A fluent if-expression for this value.
`default boolean`	`isDefined()` Checks, this `Value` is defined, i.e.
`boolean`	`isEmpty()` Checks, this `Value` is empty, i.e.
`boolean`	`isSingletonType()` States, if this value may contain (at most) one element or more than one element, like collections.
`Iterator<T>`	`iterator()` Returns a rich `javaslang.collection.Iterator`.
`<U> Value<U>`	`map(java.util.function.Function<? super T,? extends U> mapper)` Maps this value to a new value with different component type.
`default T`	`orElse(T other)` Returns the underlying value if present, otherwise `other`.
`default T`	`orElseGet(java.util.function.Supplier<? extends T> supplier)` Returns the underlying value if present, otherwise `other`.
`default <X extends Throwable> T`	`orElseThrow(java.util.function.Supplier<X> supplier)` Returns the underlying value if present, otherwise throws `supplier.get()`.
`default T`	`orElseTry(Try.CheckedSupplier<? extends T> supplier)` Returns the underlying value if present, otherwise returns the result of `Try.of(supplier).get()`.
`default void`	`out(PrintStream out)` Sends the string representations of this value to the `PrintStream`.
`default void`	`out(PrintWriter writer)` Sends the string representations of this value to the `PrintWriter`.
`Value<T>`	`peek(java.util.function.Consumer<? super T> action)` Performs the given `action` on the first element if this is an eager implementation.
`default void`	`stderr()` Sends the string representations of this value to the standard error stream System.err.
`default void`	`stdout()` Sends the string representations of this value to the standard output stream System.out.
`default Array<T>`	`toArray()` Converts this value to a `Array`.
`default CharSeq`	`toCharSeq()` Converts this value to a `CharSeq`.
`default Object[]`	`toJavaArray()` Converts this value to an untyped Java array.
`default T[]`	`toJavaArray(Class<T> componentType)` Converts this value to a typed Java array.
`default List<T>`	`toJavaList()` Converts this value to an `List`.
`default <K,V> Map<K,V>`	`toJavaMap(java.util.function.Function<? super T,? extends Tuple2<? extends K,? extends V>> f)` Converts this value to a `Map`.
`default Optional<T>`	`toJavaOptional()` Converts this value to an `Optional`.
`default Set<T>`	`toJavaSet()` Converts this value to a `Set`.
`default java.util.stream.Stream<T>`	`toJavaStream()` Converts this value to a `Stream`.
`default Lazy<T>`	`toLazy()` Converts this value to a `Lazy`.
`default List<T>`	`toList()` Converts this value to a `List`.
`default <K,V> Map<K,V>`	`toMap(java.util.function.Function<? super T,? extends Tuple2<? extends K,? extends V>> f)` Converts this value to a `Map`.
`default Option<T>`	`toOption()` Converts this value to an `Option`.
`default Queue<T>`	`toQueue()` Converts this value to a `Queue`.
`default Set<T>`	`toSet()` Converts this value to a `Set`.
`default Stack<T>`	`toStack()` Converts this value to a `Stack`.
`default Stream<T>`	`toStream()` Converts this value to a `Stream`.
`String`	`toString()` Clarifies that values have a proper toString() method implemented.
`default Tree<T>`	`toTree()` Converts this value to a `Tree`.
`default Try<T>`	`toTry()` Converts this value to a `Try`.
`default Try<T>`	`toTry(java.util.function.Supplier<? extends Throwable> ifEmpty)` Converts this value to a `Try`.
`default Vector<T>`	`toVector()` Converts this value to a `Vector`.

Methods inherited from interface javaslang.algebra.Foldable
fold, fold, foldLeft, foldMap, foldRight

Methods inherited from interface javaslang.algebra.Monad
lift, lift, lift, lift, lift, lift, lift, lift

Methods inherited from interface java.lang.Iterable
spliterator

- Method Detail
 - get
```
static <T> T get(Iterable<? extends T> iterable)
```
 Gets the first value of the given Iterable if exists, otherwise throws.
 
 Type Parameters:
 
 T - Component type
 
 Parameters:
 
 iterable - An java.lang.Iterable
 
 Returns:
 
 An object of type T
 
 Throws:
 
 NoSuchElementException - if the given iterable is empty
 - get
```
T get()
```
 Gets the underlying value or throws if no value is present.
 
 Returns:
 
 the underlying value
 
 Throws:
 
 NoSuchElementException - if no value is defined
 - getOption
```
default Option<T> getOption()
```
 Gets the underlying as Option.
 
 Returns:
 
 Some(value) if a value is present, None otherwise
 - ifDefined
```
default T ifDefined(T trueVal,
 T falseVal)
```
 A fluent if-expression for this value. If this is defined (i.e. not empty) trueVal is returned, otherwise falseVal is returned.
 
 Parameters:
 
 trueVal - The result, if this is defined.
 
 falseVal - The result, if this is not defined.
 
 Returns:
 
 trueVal if this.isDefined(), otherwise falseVal.
 - ifDefined
```
default T ifDefined(java.util.function.Supplier<? extends T> trueSupplier,
 java.util.function.Supplier<? extends T> falseSupplier)
```
 A fluent if-expression for this value. If this is defined (i.e. not empty) trueSupplier.get() is returned, otherwise falseSupplier.get() is returned.
 
 Parameters:
 
 trueSupplier - The result, if this is defined.
 
 falseSupplier - The result, if this is not defined.
 
 Returns:
 
 trueSupplier.get() if this.isDefined(), otherwise falseSupplier.get().
 - ifEmpty
```
default T ifEmpty(T trueVal,
 T falseVal)
```
 A fluent if-expression for this value. If this is empty (i.e. not defined) trueVal is returned, otherwise falseVal is returned.
 
 Parameters:
 
 trueVal - The result, if this is empty.
 
 falseVal - The result, if this is not empty.
 
 Returns:
 
 trueVal if this.isEmpty(), otherwise falseVal.
 - ifEmpty
```
default T ifEmpty(java.util.function.Supplier<? extends T> trueSupplier,
 java.util.function.Supplier<? extends T> falseSupplier)
```
 A fluent if-expression for this value. If this is empty (i.e. not defined) trueSupplier.get() is returned, otherwise falseSupplier.get() is returned.
 
 Parameters:
 
 trueSupplier - The result, if this is defined.
 
 falseSupplier - The result, if this is not defined.
 
 Returns:
 
 trueSupplier.get() if this.isEmpty(), otherwise falseSupplier.get().
 - isEmpty
```
boolean isEmpty()
```
 Checks, this Value is empty, i.e. if the underlying value is absent.
 
 Returns:
 
 false, if no underlying value is present, true otherwise.
 - isDefined
```
default boolean isDefined()
```
 Checks, this Value is defined, i.e. if the underlying value is present.
 
 Returns:
 
 true, if an underlying value is present, false otherwise.
 - isSingletonType
```
boolean isSingletonType()
```
 States, if this value may contain (at most) one element or more than one element, like collections.
 We call a type singleton type, which may contain at most one element.
 
 Returns:
 
 true, if this is a singleton type, false otherwise.
 - orElse
```
default T orElse(T other)
```
 Returns the underlying value if present, otherwise other.
 
 Parameters:
 
 other - An alternative value.
 
 Returns:
 
 A value of type T
 - orElseGet
```
default T orElseGet(java.util.function.Supplier<? extends T> supplier)
```
 Returns the underlying value if present, otherwise other.
 
 Parameters:
 
 supplier - An alternative value supplier.
 
 Returns:
 
 A value of type T
 
 Throws:
 
 NullPointerException - if supplier is null
 - orElseThrow
```
default <X extends Throwable> T orElseThrow(java.util.function.Supplier<X> supplier)
 throws X extends Throwable
```
 Returns the underlying value if present, otherwise throws supplier.get().
 
 Type Parameters:
 
 X - a Throwable type
 
 Parameters:
 
 supplier - An exception supplier.
 
 Returns:
 
 A value of type T.
 
 Throws:
 
 NullPointerException - if supplier is null
 
 X - if no value is present
 
 X extends Throwable
 - orElseTry
```
default T orElseTry(Try.CheckedSupplier<? extends T> supplier)
```
 Returns the underlying value if present, otherwise returns the result of Try.of(supplier).get().
 
 Parameters:
 
 supplier - An alternative value supplier.
 
 Returns:
 
 A value of type T.
 
 Throws:
 
 NullPointerException - if supplier is null
 
 Failure.NonFatal - containing the original exception if this Value was empty and the Try failed.
 - peek
```
Value<T> peek(java.util.function.Consumer<? super T> action)
```
 Performs the given action on the first element if this is an eager implementation. Performs the given action on all elements (the first immediately, successive deferred), if this is a lazy implementation.
 
 Parameters:
 
 action - The action that will be performed on the element(s).
 
 Returns:
 
 this instance
 - equals
```
boolean equals(Object o)
```
 Clarifies that values have a proper equals() method implemented.
 See Object.equals(Object).
 
 Overrides:
 
 equals in class Object
 
 Parameters:
 
 o - An object
 
 Returns:
 
 true, if this equals o, false otherwise
 - hashCode
```
int hashCode()
```
 Clarifies that values have a proper hashCode() method implemented.
 See Object.hashCode().
 
 Overrides:
 
 hashCode in class Object
 
 Returns:
 
 The hashcode of this object
 - toString
```
String toString()
```
 Clarifies that values have a proper toString() method implemented.
 See Object.toString().
 
 Overrides:
 
 toString in class Object
 
 Returns:
 
 A String representation of this object
 - filter
```
Value<T> filter(java.util.function.Predicate<? super T> predicate)
```
 Description copied from interface: Monad
 
 Filters this Monad by testing a predicate.
 The semantics may vary from class to class, e.g. for single-valued type (like Option) and multi-values types (like Traversable). The commonality is, that filtered.isEmpty() will return true, if no element satisfied the given predicate.
 Also, an implementation may throw NoSuchElementException, if no element makes it through the filter and this state cannot be reflected. E.g. this is the case for Either.LeftProjection and Either.RightProjection.
 
 Specified by:
 
 filter in interface Monad<T>
 
 Parameters:
 
 predicate - A predicate
 
 Returns:
 
 a new Monad instance
 - flatMap
```
 Value flatMap(java.util.function.Function<? super T,? extends Iterable<? extends U>> mapper)
```
 Description copied from interface: Monad
 FlatMaps this value to a new value with different component type.
 FlatMap is the sequence operation for functions and behaves like the imperative ;.
 If the previous results are needed, flatMap cascades:
```
 
 m1().flatMap(result1 ->
 m2(result1).flatMap(result2 ->
 m3(result1, result2).flatMap(result3 ->
 ...
 )
 )
 );
 
 
```
 If only the last result is needed, flatMap may be used sequentially:
```
 
 m1().flatMap(this::m2)
 .flatMap(this::m3)
 .flatMap(...);
 
 
```
 Specified by:
 
 flatMap in interface Monad<T>
 
 Type Parameters:
 
 U - Component type of the mapped Monad
 
 Parameters:
 
 mapper - A mapper
 
 Returns:
 
 a mapped Monad
 - foldLeft
```
default  U foldLeft(U zero,
 java.util.function.BiFunction<? super U,? super T,? extends U> combine)
```
 Description copied from interface: Foldable
 
 Folds this elements from the left, starting with zero and successively calling combine.
 
 Specified by:
 
 foldLeft in interface Foldable<T>
 
 Type Parameters:
 
 U - the type of the folded value
 
 Parameters:
 
 zero - A zero element to start with.
 
 combine - A function which combines elements.
 
 Returns:
 
 a folded value
 - foldRight
```
default  U foldRight(U zero,
 java.util.function.BiFunction<? super T,? super U,? extends U> combine)
```
 Description copied from interface: Foldable
 
 Folds this elements from the right, starting with zero and successively calling combine.
 
 Specified by:
 
 foldRight in interface Foldable<T>
 
 Type Parameters:
 
 U - the type of the folded value
 
 Parameters:
 
 zero - A zero element to start with.
 
 combine - A function which combines elements.
 
 Returns:
 
 a folded value
 - map
```
 Value map(java.util.function.Function<? super T,? extends U> mapper)
```
 Description copied from interface: Monad
 
 Maps this value to a new value with different component type.
 
 Specified by:
 
 map in interface Functor<T>
 
 Specified by:
 
 map in interface Monad<T>
 
 Type Parameters:
 
 U - Component type of the mapped Monad
 
 Parameters:
 
 mapper - A mapper
 
 Returns:
 
 a mapped Monad
 - toArray
```
default Array<T> toArray()
```
 Converts this value to a Array.
 
 Returns:
 
 A new Array.
 - toCharSeq
```
default CharSeq toCharSeq()
```
 Converts this value to a CharSeq.
 
 Returns:
 
 A new CharSeq.
 - toJavaArray
```
default T[] toJavaArray(Class<T> componentType)
```
 Converts this value to a typed Java array.
 
 Parameters:
 
 componentType - Component type of the array
 
 Returns:
 
 A new Java array.
 - toJavaList
```
default List<T> toJavaList()
```
 Converts this value to an List.
 
 Returns:
 
 A new ArrayList.
 - toJavaMap
```
default <K,V> Map<K,V> toJavaMap(java.util.function.Function<? super T,? extends Tuple2<? extends K,? extends V>> f)
```
 Converts this value to a Map.
 
 Type Parameters:
 
 K - The key type
 
 V - The value type
 
 Parameters:
 
 f - A function that maps an element to a key/value pair represented by Tuple2
 
 Returns:
 
 A new HashMap.
 - toJavaOptional
```
default Optional<T> toJavaOptional()
```
 Converts this value to an Optional.
 
 Returns:
 
 A new Optional.
 - toJavaSet
```
default Set<T> toJavaSet()
```
 Converts this value to a Set.
 
 Returns:
 
 A new HashSet.
 - toJavaStream
```
default java.util.stream.Stream<T> toJavaStream()
```
 Converts this value to a Stream.
 
 Returns:
 
 A new Stream.
 - toLazy
```
default Lazy<T> toLazy()
```
 Converts this value to a Lazy.
 
 Returns:
 
 A new Lazy.
 - toList
```
default List<T> toList()
```
 Converts this value to a List.
 
 Returns:
 
 A new List.
 - toMap
```
default <K,V> Map<K,V> toMap(java.util.function.Function<? super T,? extends Tuple2<? extends K,? extends V>> f)
```
 Converts this value to a Map.
 
 Type Parameters:
 
 K - The key type
 
 V - The value type
 
 Parameters:
 
 f - A function that maps an element to a key/value pair represented by Tuple2
 
 Returns:
 
 A new HashMap.
 - toOption
```
default Option<T> toOption()
```
 Converts this value to an Option.
 
 Returns:
 
 A new Option.
 - toQueue
```
default Queue<T> toQueue()
```
 Converts this value to a Queue.
 
 Returns:
 
 A new Queue.
 - toSet
```
default Set<T> toSet()
```
 Converts this value to a Set.
 
 Returns:
 
 A new HashSet.
 - toStack
```
default Stack<T> toStack()
```
 Converts this value to a Stack.
 
 Returns:
 
 A new List, which is a Stack.
 - toStream
```
default Stream<T> toStream()
```
 Converts this value to a Stream.
 
 Returns:
 
 A new Stream.
 - toTry
```
default Try<T> toTry()
```
 Converts this value to a Try.
 If this value is undefined, i.e. empty, then a new Failure(NoSuchElementException) is returned, otherwise a new Success(value) is returned.
 
 Returns:
 
 A new Try.
 - toTry
```
default Try<T> toTry(java.util.function.Supplier<? extends Throwable> ifEmpty)
```
 Converts this value to a Try.
 If this value is undefined, i.e. empty, then a new Failure(ifEmpty.get()) is returned, otherwise a new Success(value) is returned.
 
 Parameters:
 
 ifEmpty - an exception supplier
 
 Returns:
 
 A new Try.
 - toTree
```
default Tree<T> toTree()
```
 Converts this value to a Tree.
 
 Returns:
 
 A new Tree.
 - toVector
```
default Vector<T> toVector()
```
 Converts this value to a Vector.
 
 Returns:
 
 A new Vector.
 - out
```
default void out(PrintStream out)
```
 Sends the string representations of this value to the PrintStream. If this value consists of multiple elements, each element is displayed in a new line.
 
 Parameters:
 
 out - The PrintStream to write to
 - out
```
default void out(PrintWriter writer)
```
 Sends the string representations of this value to the PrintWriter. If this value consists of multiple elements, each element is displayed in a new line.
 
 Parameters:
 
 writer - The PrintWriter to write to
 - iterator
```
Iterator<T> iterator()
```
 Returns a rich javaslang.collection.Iterator.
 
 Specified by:
 
 iterator in interface Iterable<T>
 
 Returns:
 
 A new Iterator
 - corresponds
```
default  boolean corresponds(Iterable that,
 java.util.function.BiPredicate<? super T,? super U> predicate)
```
 Tests whether every element of this iterable relates to the corresponding element of another iterable by satisfying a test predicate.
 
 Type Parameters:
 
 U - Component type of that iterable
 
 Parameters:
 
 that - the other iterable
 
 predicate - the test predicate, which relates elements from both iterables
 
 Returns:
 
 true if both iterables have the same length and predicate(x, y) is true for all corresponding elements x of this iterable and y of that, otherwise false.
 - eq
```
default boolean eq(Object o)
```
 A smoothing replacement for equals. It is similar to Scala's == but better in the way that it is not limited to collection types, e.g. Some(1) eq List(1), None eq Failure(x) etc.
 In a nutshell: eq checks congruence of structures and equality of contained values.
 Example:
```
 // ((1, 2), ((3))) => structure: (()(())) values: 1, 2, 3
 final Iterable<?> i1 = List.of(List.of(1, 2), Arrays.asList(List.of(3)));
 final Iterable<?> i2 = Queue.of(Stream.of(1, 2), List.of(Lazy.of(() -> 3)));
 assertThat(i1.eq(i2)).isTrue();
 
```
 Semantics:
```
 o == this : true
 o instanceof javaslang.Iterable : iterable elements are eq, non-iterable elements equals, for all (o1, o2) in (this, o)
 o instanceof java.lang.Iterable : this eq Iterator.of((java.lang.Iterable<?>) o);
 otherwise : false
 
```
 Parameters:
 
 o - An object
 
 Returns:
 
 true, if this equals o according to the rules defined above, otherwise false.
 - exists
```
default boolean exists(java.util.function.Predicate<? super T> predicate)
```
 Checks, if an element exists such that the predicate holds.
 
 Parameters:
 
 predicate - A Predicate
 
 Returns:
 
 true, if predicate holds for one or more elements, false otherwise
 
 Throws:
 
 NullPointerException - if predicate is null
 - forAll
```
default boolean forAll(java.util.function.Predicate<? super T> predicate)
```
 Checks, if the given predicate holds for all elements.
 
 Parameters:
 
 predicate - A Predicate
 
 Returns:
 
 true, if the predicate holds for all elements, false otherwise
 
 Throws:
 
 NullPointerException - if predicate is null
 - forEach
```
default void forEach(java.util.function.Consumer<? super T> action)
```
 Performs an action on each element.
 
 Specified by:
 
 forEach in interface Iterable<T>
 
 Parameters:
 
 action - A Consumer
 
 Throws:
 
 NullPointerException - if action is null
 - toJavaArray
```
default Object[] toJavaArray()
```
 Converts this value to an untyped Java array.
 
 Returns:
 
 A new Java array.
 - stderr
```
default void stderr()
```
 Sends the string representations of this value to the standard error stream System.err. If this value consists of multiple elements, each element is displayed in a new line.
 
 Throws:
 
 IllegalStateException - if PrintStream.checkError() is true after writing to stderr.
 - stdout
```
default void stdout()
```
 Sends the string representations of this value to the standard output stream System.out. If this value consists of multiple elements, each element is displayed in a new line.
 
 Throws:
 
 IllegalStateException - if PrintStream.checkError() is true after writing to stdout.

Interface Value<T>

Method Summary

Methods inherited from interface javaslang.algebra.Foldable

Methods inherited from interface javaslang.algebra.Monad

Methods inherited from interface java.lang.Iterable

Method Detail

get

get

getOption

ifDefined

ifDefined

ifEmpty

ifEmpty

isEmpty

isDefined

isSingletonType

orElse

orElseGet

orElseThrow

orElseTry

peek

equals

hashCode

toString

filter

flatMap

foldLeft

foldRight

map

toArray

toCharSeq

toJavaArray

toJavaList

toJavaMap

toJavaOptional

toJavaSet

toJavaStream

toLazy

toList

toMap

toOption

toQueue

toSet

toStack

toStream

toTry

toTry

toTree

toVector

out

out

iterator

corresponds

eq

exists

forAll

forEach

toJavaArray

stderr

stdout