Streams

Question 1

What is a Stream

Answer 1

Stream provides manipulation of Java collections in a declarative way. Think stream is like a fancy iterator over collection.

Question 2

what exactly is a stream?

Answer 2

“a sequence of elements from a

source that supports data-processing operations.”

Question 3

Pipelining in stream?

Answer 3

Many stream operations return a stream themselves, allowing operations to be chained to form a larger pipeline.This enables certain optimizations
that we explain , such as laziness and short-circuiting.

Question 4

How many times stream can be traversed?

Answer 4

Note that, similarly to iterators, a stream can be traversed only once. it will throw java.lang.IllegalStateException: stream has already been operated upon or closed.

Question 5

Stream operations Categories?

Answer 5

The streams interface in java.util.stream.Stream defines many operations. They can be classified into two categories. Stream operations that can be connected are called intermediate operations, and operations
that close a stream are called terminal operations.

Question 6

What are Intermediate operations?

Answer 6

Intermediate operations such as filter or sorted return another stream as the return type. This allows the operations to be connected to form a query. What’s important is that intermediate operations don’t perform any processing until a terminal operation is invoked on the stream pipeline—they’re lazy. This is because intermediate operations can usually be merged and processed into a single pass by the terminal operation.

Question 7

What are Terminal operations?

Answer 7

Terminal operations produce result from a stream pipeline.

a result is any non stream value such as a List, an Integer , or even a void.

Question 8

In the stream pipeline that follows, can you identify the intermediate and terminal
operations?

long count = menu.stream()
.filter(dish -> dish.getCalories() > 300)
.distinct()
.limit(3)
.count();

Answer 8

The last operation in the stream pipeline count returns a long, which is a non-stream
value. It’s therefore a terminal operation. All previous operations, filter, distinct,
limit, are connected and return a stream. They are therefore intermediate operations.

Question 9

Summary

Answer 9

A stream is a sequence of elements from a source that supports data-processing
operations.
 Streams make use of internal iteration: the iteration is abstracted away through
operations such as filter, map, and sorted.
 There are two types of stream operations: intermediate and terminal operations.
 Intermediate operations such as filter and map return a stream and can be
chained together. They’re used to set up a pipeline of operations but don’t produce
any result.
 Terminal operations such as forEach and count return a non-stream value and
process a stream pipeline to return a result.
 The elements of a stream are computed on demand (“lazily”).