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It seems like the Optional in Java 8 is a monad.
Are the Streams also monads?
Can anyone identify the endofunctor and the two natural transformations in the optional monad?
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Java 8 offers the possibility to create streams out of three primitive types: int, long and double. As Stream<T> is a generic interface, and there is no way to use primitives as a type parameter with generics, three new special interfaces were created: IntStream, LongStream, DoubleStream.
A monad is just a wrapper around a type or data structure. So by 'wrapping' a class type (e.g. Integer) inside the Java Optional type, we add some functionality around it, like of(x) , isPresent() , orElse(c) and get() . To be more precise, a Monad always contains a bind() function, That translates to flatMap in Java.
Introduced in Java 8, the Stream API is used to process collections of objects. A stream is a sequence of objects that supports various methods which can be pipelined to produce the desired result. A stream is not a data structure instead it takes input from the Collections, Arrays or I/O channels.
Streams are lazy because intermediate operations are not evaluated until terminal operation is invoked. Each intermediate operation creates a new stream, stores the provided operation/function and return the new stream. The pipeline accumulates these newly created streams.
To understand this material, you need to have a basic, working knowledge of Java 8 (lambda expressions, Optional, method references). First of all, Java 8 Streams should not be confused with Java I/O streams (ex: FileInputStream etc); these have very little to do with each other.
List is not a monad in Java, but we can easily create it, or we can get a Stream from a list, and Stream is a monad. We may also use monads to deal with future values, and even for primitives wrappers. In Java 8, the Collection.stream() method may be used to transform a collection into a monad.
Introduced in Java 8, the Stream API is used to process collections of objects. A stream is a sequence of objects that supports various methods which can be pipelined to produce the desired result.
We can also obtain a stream from an existing list: Note that Java 8 added a new stream () method to the Collection interface. And we can create a stream from individual objects using Stream.of (): Or simply using Stream.builder (): There are also other ways to obtain a stream, some of which we will see in sections below.
EDIT The answer below is incorrect (retained here for history).
Yes, in each case the functor consists of the class and its
mapmethod, and the two natural transformations areofandflatMap(identity).
The correct answer seems to be here.
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answered Oct 02 '22 13:10
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