package stream.util;

import function.BiFunction;

import function.Supplier;

import stream.Collector;

import java.util.ArrayList;

import java.util.HashSet;

import java.util.List;

import java.util.Set;

import java.util.function.Function;

/**

* @Author xiongyx

* on 2019/3/10.

*

* stream.collect() 参数常用工具类

*/

public class CollectUtils {

/**

* stream 转换为 List

* */

public static <T> Collector<T, List<T>, List<T>> toList(){

return new Collector<T, List<T>, List<T>>() {

@Override

public Supplier<List<T>> supplier() {

return ArrayList::new;

}

@Override

public BiFunction<List<T>, List<T>, T> accumulator() {

return (list, item) -> {

list.add(item);

return list;

};

}

@Override

public Function<List<T>, List<T>> finisher() {

return list -> list;

}

};

}

/**

* stream 转换为 Set

* */

public static <T> Collector<T, Set<T>, Set<T>> toSet(){

return new Collector<T, Set<T>, Set<T>>() {

@Override

public Supplier<Set<T>> supplier() {

return HashSet::new;

}

@Override

public BiFunction<Set<T>, Set<T>, T> accumulator() {

return (set, item) -> {

set.add(item);

return set;

};

}

@Override

public Function<Set<T>, Set<T>> finisher() {

return set -> set;

}

};

}

}