자바 익숙히 할 표현법들(스트림 라이브러리, 그래프표현법 등등)

Implementations of Collector that implement various useful reduction operations, such as accumulating elements into collections, summarizing elements according to various criteria, etc.

The following are examples of using the predefined collectors to perform common mutable reduction tasks:

// Accumulate names into a List
List<String> list = people.stream()
.map(Person::getName)
.collect(Collectors.toList());

// Accumulate names into a TreeSet
Set<String> set = people.stream()
.map(Person::getName)
.collect(Collectors.toCollection(TreeSet::new));

// Convert elements to strings and concatenate them, separated by commas
String joined = things.stream()
.map(Object::toString)
.collect(Collectors.joining(", "));

// 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));

 

 

////                List<List<Edge>> G = new ArrayList<>(N);
////                for (int i = 0; i < N; ++i) G.add(new ArrayList<Edge>());
////                //List<Edge>[] G2=new ArrayList[N+1];위와 같은 표현
////                //for (int i = 0; i < G2.length; i++) G2[i] = new ArrayList<>();