How to use Map in Java 8
Map is a well known functional programming concept which is incorporated into Java 8. Map is a function defined in
java.util.stream.Streams class, which is used to transform each element of stream. Because of this property you can use Map in Java 8 to transform a
Collection,
List,
Set or
Map.
For example, if you have a list of String and you want to convert all
of them into upper case, how will you do this? Prior to Java 8, there is
no function to do this. You had to iterate through List using a for
loop or foreach loop and transform each element. In Java 8, you get stream, which allow you to
apply many functional programming operator like map, reduce and filter. By using Map function you can apply any function to every element of
Collection.
It can be any predefined function or a user defined function. You not
only can use lambda expression but also you can also use method
references. Some examples of Map in Java 8 is to convert a list of
integers
and then square of each number. Map function is also an intermediate
operation and it return a stream of transformed element. Stream API also
provides methods like
mapToDouble(),
mapToInt(), and
mapToLong() which returns
DoubleStream,
IntStream and
LongStream, which are specialized stream for
double,
int and
long data types. You can collect the result of transformation by using
Collectors class, which provides several method to collect the result of transformation into
List,
Set or any
Collection.
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