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Java 8 - Streams - Collectors - Summing




  • summing operation on Collectors provides a way to aggregate the result of a stream operation into a number.
  • The different implementations yield Integer, Double and Long which are summingInt, summingDouble, summingLong respectively.

stream of employees
Stream employees = Stream.of( new Employee("Joe", "Blogs", "Sales", 100.0), new Employee("Richardo", "Banks", "Engineering", 50.0), new Employee("Hewlet", "Packer", "Warehouse", 40.0) );


USAGE

collecting stream transformation result in a Double

Double summedSalaries = employees .filter(employee -> employee.getLastName().startsWith("B")) .collect(Collectors.summingDouble(Employee::getSalary));

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