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Stream API in Java

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Nitish Sonkar
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Stream API in Java

It can be classify into two operation.

  1. Intermediate operation

    Transform a stream into another stream.

    Examples: filter, map, distinct, sorted, limit, etc.

  2. Terminal operation

    It's provide the result and terminate the stream.

    Example: forEach, collect, reduce, count, toArray, etc.

The Java 8 Stream API Tutorial

Filter

syntax: 
Stream filteredSteream=orinalStream.filter(element->/*predicate*/);

Predicate: It returns true or false

Question: Find out even number from the arrayList using Stream?

List<Integer> list = Arrays.asList(4,5,6,7);
List<Integer> filteredList= list.stream().filter(n->n%2==0).toList();

input: 10 elements

output: 0 to 10 elements

Map

syntax: 
Stream filteredSteream=orinalStream.map(element->/*transformation fuction*/);

Predicate: It returns true or false

It takes function as an argument, return type is based on type of data.

Question: Multiply by 2 to each element from a list?

List<Integer> list = Arrays.asList(4,5,6,7);
List<Integer> mapList= list.stream().map(n->n*2).toList();

Question: Select only passed students and add 5 grace mark to all failed students?

input: 10 elements

output: 10 elements

Count

To count the number of element in the stream.

Question: Find out total number of failed students?

Sorted

To sort order of element in stream.

Sorting in descending order

Customizing the sorting order then you have to use Comparator. Comparator is functional Interface. It has a compare(obj1, obj2) method. you can also use lambda expression.

return -ve: obj1 has come before obj2
return +ve: obj1 has come after obj2;

min() and max()

toArray()

stream Api