collectors排序_java8特性：Collectors.groupingBy进行分组、排序等操做 (二)

Stream类的函数java

R collect(Collector super T, A, R> collector);

能够对数据集进行简单的分组统计。函数参数为接口Collector,其实如今final class Collectors的内部静态类CollectorImpl。Collector接口代码以下：web

public interface Collector {

Supplier supplier();

BiConsumer accumulator();

BinaryOperator combiner();

Function finisher();

Set characteristics();

public static Collector of(Supplier supplier,

BiConsumer accumulator,

BinaryOperator combiner,

Characteristics... characteristics) {

Objects.requireNonNull(supplier);

Objects.requireNonNull(accumulator);

Objects.requireNonNull(combiner);

Objects.requireNonNull(characteristics);

Set cs = (characteristics.length == 0)

? Collectors.CH_ID

: Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.IDENTITY_FINISH,

characteristics));

return new Collectors.CollectorImpl<>(supplier, accumulator, combiner, cs);

}

public static Collector of(Supplier supplier,

BiConsumer accumulator,

BinaryOperator combiner,

Function finisher,

Characteristics... characteristics) {

Objects.requireNonNull(supplier);

Objects.requireNonNull(accumulator);

Objects.requireNonNull(combiner);

Objects.requireNonNull(finisher);

Objects.requireNonNull(characteristics);

Set cs = Collectors.CH_NOID;

if (characteristics.length > 0) {

cs = EnumSet.noneOf(Characteristics.cl