How to use a Java stream.

A Java stream reminds me of Spark SQL when using the dot notation. In IntelliJ, you can see the type of each nested method.

For example in this Then step from Cucumber

@Then("A list of digits is extracted")
public void a_list_of_digits_is_extracted(DataTable dataTable) {
	List<Integer> expectedDigits = dataTable.asLists()
		.get(0)
		.stream()
		.map(Integer::parseInt)
		.toList();

IntelliJ shows the type of the variable on the right side of each method

  • dataTable.asLists()…List<List<String>>
  • .get(0)…List<String>
  • .stream()…Stream<String>
  • .map(Integer::parseInt)…Stream<Integer>

Use a Java stream to filter or change/map the data.

someArrayOfIntegerNumbers.stream()
	.filter(OddNumber::isOdd)
	.toList();

someArrayOfStringNumbers.stream()
	.map(Integer::parseInt)
	.toList();