Java Streams

• Added in Java 8
• Wrapper around a data source, allowing us to operate on that data source and make bulk processing fast
• Stream doesn’t store data (not a data structure)
• Does not modifying underling data source
• java.util.stream supports functional style operations such as map-reduce transformations on collections

Stream Creation:

Below are 3 popular methods to create a java Stream.

1)

collection.stream() -: eg: emparray.stream()

2)

Stream.of(emparray[0], emparray[1], emparray[2]);

3)

StreamBuilder empStreamBuilder = Stream.builder(); empStreamBuilder.accept(emparray[0]); empStreamBuilder.accept(emparray[1]); empStreamBuilder.accept(emparray[2]);

Stream empStream = empStreamBuilder.build();

Stream Operations:

forEach — loops over the stream elements, calling the supplied function on each element.

The below code effectively calls incrementSalary on each element of empList.

@Test public void whenIncrementSalaryForEachEmployee_thenApplyNewSalary() { empList.stream().forEach(e -> e.incrementSalary(10.00)); assertThat(empList, contains( hasProperty("salary",110000), hasProperty("salary", 210000), hasProperty("salary", 3100000) ));