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FUNCTIONAL
PROGRAMMING
2024
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DIRECT APPLICATION
This guide is designed for you
to be able to apply it right
away
SUMMARY
In this quick guide, we will
explain in simple terms what
functional programming
paradigm is and how to apply
it using Java Streams.
12 mins read
FUNCTIONAL PROGRAMMING
In simple terms, functional
programming is a coding style where
you build programs by combining
functions that don't change the
program's state and always produce the
same output for the same input.
It is like using building blocks, where
each block is a function that does a
specific job without affecting the other
blocks, and you can combine them in
different ways to build your program.
Don’t worry this is just the definition you
will understand it more once we discuss
the examples.
So let’s jump right in...
JAVA STREAMS
Java Streams provide a way to efficiently
process large amounts of data by
allowing you to define a sequence of
operations to be applied on a collection
of objects, like filtering, sorting, or
summing up values.
to use streams you should do the
following:
1. convert list to stream by using
stream() method
2. apply specific stream methods
3. convert back to list using toList()
we’ll be showing the top use cases of
Java Streams in the following pages...
FILTER
Purpose: Filters elements based on a
condition.
EXAMPLE:
In the code above we are creating an
array called names.
Then we are filtering names based on a
condition that the name should start
with letter ‘A’
finally, we are converting it back to a list
and saving it in method filteredNames
MAP
Purpose: Transforms each element in
the stream.
EXAMPLE:
map simply changes each item in the
array to another according to the
lambda method we pass.
So, in the code above we are mapping
each element to element * element.
sqauredNumbers will be 1, 4, 9
SORTED
Purpose: Sorts the elements of the
stream.
EXAMPLE:
sorted simple sorts the array in
alphabatical order.
so sortedNames will be ["Alice", "Bob",
"Charlie"]
LIMIT
Purpose: Limits the number of
elements in the stream.
EXAMPLE:
Limit comes in handy in many places
where you want to limit the number of
items you want to take from a list.
In the code above, the output will be:
[1, 2, 3, 4, 5]
REDUCE
Purpose: Performs a reduction on the
elements of the stream to produce a
single cumulative result.
EXAMPLE:
As its name indicates it reduces the list of
items to a single result.
In the code above, we are reducing the list of
items to one number which is its sum.
we pass the reduce:
0: This is the initial value. The reduce
operation starts with this value.
(a, b) -> a + b: This is a lambda expression.
Here, it describes how to combine two
elements. a is the accumulated result so
far, and b is the value of the current
element in the stream.
For each element in the stream, the
lambda expression is applied. It adds the
current element (b) to the accumulated
sum (a).
CONCATENATING METHODS
Purpose: do multiple operations on the
same list of items.
EXAMPLE:
you can do multiple operations on the
same list.
In the code above, we are:
1. sorting the array
output: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
2. limiting it to first 5 items
output: [1, 2, 3, 4, 5]
3. multiplying each element by itself
final output: [1, 4, 9, 16, 25]
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