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Module java.base
Package java.util.stream
Class Collectors
java.lang.Object
java.util.stream.Collectors
public final class Collectors
extends Object
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 list = people.stream()
.map(Person::getName)
.collect(Collectors.toList());
// Accumulate names into a TreeSet
Set 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 byDept = employees.stream()
.collect(Collectors.groupingBy(Employee::getDepartment));
// Compute sum of salaries by department
Map totalByDept = employees.stream()
.collect(Collectors.groupingBy(Employee::getDepartment,
Collectors.summingInt(Employee::getSalary)));
// Partition students into passing and failing
Map passingFailing = students.stream()
.collect(Collectors.partitioningBy(s -> s.getGrade() >= PASS_THRESHOLD));
Since:
1.8
Method Summary
All Methods Static Methods Concrete Methods
Modifier and Type
Method
Description
static Collector
averagingDouble(ToDoubleFunction |