Chapter 5 - Functional processing of collections (optional)) Flashcards
describe
imperative programming
this programming style is where we write a series of statements/commands that each change the change the state of an object.
We are concerned and know how each step is taken to achieve the result
example:
ArrayList<int> temp = new ArrayList<>();
For(int element : collection){
Temp1 = Element * 2;
Temp.add(temp1);
}
Return temp;
features include:
1.Is a method of a collection
2.Will remove elements from the collection if the predicate returns true
give 2 features of the method
removeIf()
examples include:
1.adding up all values from the stream
2.Concatenating characters from a stream to create a string
3.Picking the smallest or largest value from a stream
give 3 examples of
reducing
this operates by:
1.Takes a stream as input
2.Creates a new element from the original element (can be a change in type or content)
3.Creates a new stream as its output
explain in 3 steps how the stream method
map()
operates
syntax:
filter(lambda expression)
what is the syntax for the method
filter()
a lambda contains one parameter and two statements
what is the syntax for writing this
the syntax is:
param1 -> {statement1; statement2;}
note: this rule applies the other way i.e 2param and 1 statement
reasons include:
1.They provide methods that we might commonly carry out on collections
2.these are safe when applying parallel processing
3.Using these means that we do not need to explicitly create a loop
give 3 reasons as to why
streams are usefull
the syntax is:
param1 -> {statement1; statement2;}
note: this rule applies the other way i.e 2param and 1 statement
a lambda contains one parameter and two statements
what is the syntax for writing this
a lambda contains one parameters and one statements
what is the syntax for writing this
the syntax is:
param1 -> statement 1
what is the syntax for the collection method
removeIf()
when used in a stream
syntax:
removeIf(predicateLambda)
example:
removeIf(element -> element.value > 10)
the code is:
countries.forEach(country -> System.out.println(country));
write the code that uses the collections forEach() method and prints a collection of strings.
the collections name is countries
write the following code:
1. create a stream from the collection animals
2. filter out the animals with name elephant
3. print the name of the filtered animals
animals has a getter method named getName() that returns a string
code:
animals.stream()
.filter(animal -> animal.getName().equals("elephant"))
.forEach(animal -> System.out.println(animal));
syntax:
limit(long maxSize)
parameters:
@param maxSize the number of elements the output stream should be limited to
what are the syntax and paramters of the stream method
limit()
syntax:
Map(lambda expression)
what is the syntax for the stream method
map()
how does the stream method
filter()
operate
This operates by:
1.Taking a stream as input
2.Evaluating each element of the stream (only an evaluation to true will get past the filter)
3.Creating a new stream as output that is composed of those that survived step 2
these include:
1.Lamdas are code but are not executed immediately
2.Lamdas do not belong to a class like methods do
3.There is no access modifier a lambda is assumed public
4.Lamdas do not declare a return type. Instead it is the job of the compiler to work this out
5.Lambdas do not have names (anonymous function)
give 5 points concerning
lambdas
code:
animals.stream()
.filter(animal -> animal.getName().equals("elephant"))
.forEach(animal -> System.out.println(animal));
write the following code:
1. create a stream from the collection animals
2. filter out the animals with name elephant
3. print the name of the filtered animals
animals has a getter method named getName() that returns a string
this is composed of two or more stream operations which are chained together.
1.a source of the stream
2.at least one intermediate stream operation
3.a terminal stream operation
syntax:
Source().inter1().inter2().inter3().terminal();
describe a
pipeline
write the code that uses the collections forEach() method and prints a collection of strings.
the collections name is countries
the code is:
countries.forEach(country -> System.out.println(country));
this is a stream operation that will take an element and using that element transform it into a specific piece of data we are interested in
describe the method
map()
give 2 points describe
lambdas
- this is similar to a method except that it is more concise and has some pre defined rules
- these can be passed as arguments just as objects can be, they will then be stored and executed when required
these are an alternative way of processing collections. they provide their own methods that allow us to manipulate data in a functional style of programming
describe a
stream
This operates by:
1.Taking a stream as input
2.Evaluating each element of the stream (only an evaluation to true will get past the filter)
3.Creating a new stream as output that is composed of those that survived step 2
how does the stream method
filter()
operate
syntax for this is:
(param1, param2) -> {statement1; statement2;}
a lambda contains two parameters and two statements
what is the syntax for writing this
these include:
1. usefull for simple, one off tasks that do not require the complexity of a full class
2. can be helpfull when creating declarative/functional style programs
give 2
use cases for lambdas
how do we
return data from a stream
When we wish to return data from a stream we must put return at the start of the stream
Example:
Return collection.stream()
.filter(lambda)
.map(lambda)
.reduce(identity, lambda)
describe how the collection method
removeIf()
works
this works by:
If the predicate returns true then current element is removed from the colllection
this is a method that is built into java collections. it is used so that we can iterate the collection and perform some operation on each element
describe the method
forEach()
A style of programming in which we specifywhatwe want done rather thanhowit should be done.
We are not concerned with how the result is achieved
example:
.map(element -> element * 2)
describe
declarative programming
this is a stream method that will take all data coming from a stream and callapse it into a single value
describe the method
reduce()
describe the method
limit()
This is an intermediate stream method that will limit the number of elements in the stream to a given number.
describe a
predicate
is afunctionthat takes at least oneargumentand returns a boolean.
describe the
difference between a method and a function
the difference between these is that a method will belong to an object where as a function does not
what is the syntax for the method
filter()
syntax:
filter(lambda expression)
give 3 reasons as to why
streams are usefull
reasons include:
1.They provide methods that we might commonly carry out on collections
2.these are safe when applying parallel processing
3.Using these means that we do not need to explicitly create a loop
syntax:
collection.stream()
what is the syntax to
create a stream from a collection
describe the method
map()
this is a stream operation that will take an element and using that element transform it into a specific piece of data we are interested in
This is an intermediate stream method that will limit the number of elements in the stream to a given number.
describe the method
limit()
the syntax is:
param1 -> statement 1
a lambda contains one parameters and one statements
what is the syntax for writing this
describe
functional programming
this style of programming is a form of declarative programming and uses a series of functions that will each change/transform data and then return it, allowing allow the next function to work on the transformed data.
this style of programming is a form of declarative programming and uses a series of functions that will each change/transform data and then return it, allowing allow the next function to work on the transformed data.
describe
functional programming
