String joining in Java 8 and more

So trivial — but I’m still discovering new features such as this in Java 8.

String message = String.join("_", "Java", "8", "is", "neat");

Returns “Java_8_is_neat”.

Also check out StringJoiner, which when used with streams you can use like this:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4);
 String commaSeparatedNumbers = numbers.stream()
     .map(i -> i.toString())
     .collect(Collectors.joining(", "));

Also check out java.util.Stream.Collectors, which makes Java 8 even more interesting. Some examples below.

// Compute sum of salaries of employee
     int total = employees.stream()
                          .collect(Collectors.summingInt(Employee::getSalary)));

     // Group employees by department
     Map<Department, List<Employee>> byDept
         = employees.stream()
                    .collect(Collectors.groupingBy(Employee::getDepartment));

     // Compute sum of salaries by department
     Map<Department, Integer> totalByDept
         = employees.stream()
                    .collect(Collectors.groupingBy(Employee::getDepartment,
                                                   Collectors.summingInt(Employee::getSalary)));

     // Partition students into passing and failing
     Map<Boolean, List<Student>> passingFailing =
         students.stream()
                 .collect(Collectors.partitioningBy(s -> s.getGrade() >= PASS_THRESHOLD));

Neat huh. (Note, these examples came from the JDK manual)