java stream collect(Supplier,BiConsumer,BiConsumer)

<R> R collect(Supplier<R> supplier,
              BiConsumer<R,? super T> accumulator,
              BiConsumer<R,R> combiner)

Parameter 1: supplierThe getmethod of the interface , which provides a container (List, Map, Set) as the parameter of the accumulator and combiner, and is the final return value (the same as the R generic constraint).
Parameter 2: accumulatorThe acceptmethod of the interface handles the supplier The provided R type container, and the elements in the stream, such as adding elements to the container. Local aggregation of the stream.
Parameter 3: combinerInterface acceptmethod to process the locally accumulatorgenerated R type container. Global aggregation of the local results

There are three ways to write, pay attention to the correspondence between

1. Use the implementation class example

package com;

import java.util.LinkedList;
import java.util.List;
import java.util.function.BiConsumer;
import java.util.function.Supplier;

public class App2 {
    
    
    public static void main(String[] args) {
    
    
        LinkedList<Integer> integers = new LinkedList<>();
        integers.add(1);
        integers.add(2);
        integers.add(3);
        List res = integers.stream().collect(
                new Supplier<List>() {
    
    
                    @Override
                    public List get() {
    
    
                        return new LinkedList();
                    }
                },
                new BiConsumer<List, Integer>() {
    
    
                    @Override
                    public void accept(List list, Integer integer) {
    
    
                        list.add(integer);
                    }
                },
                new BiConsumer<List, List>() {
    
    
                    @Override
                    public void accept(List list, List list2) {
    
    
                        list.addAll(list2);
                    }
                }
        );
        System.out.println(res);
    }
}

2. Use the lambda example

package com;

import java.util.LinkedList;
import java.util.List;

public class App2 {
    
    
    public static void main(String[] args) {
    
    
        LinkedList<Integer> integers = new LinkedList<>();
        integers.add(1);
        integers.add(2);
        integers.add(3);
        List res = integers.stream().collect(
                ()->new LinkedList(),
                (list, integer) -> list.add(integer),
                (list1,list2) -> list1.addAll(list2)
        );
        System.out.println(res);
    }
}

3. Use method reference

package com;

import java.util.LinkedList;
import java.util.List;

public class App2 {
    
    
    public static void main(String[] args) {
    
    
        LinkedList<Integer> integers = new LinkedList<>();
        integers.add(1);
        integers.add(2);
        integers.add(3);
        List res = integers.stream().collect(
                LinkedList::new,
                List::add,
                List::addAll
        );
        System.out.println(res);
    }
}

Reference:
https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#collect-java.util.function.Supplier-java.util.function.BiConsumer-java. util.function.BiConsumer-

java stream collect(Supplier,BiConsumer,BiConsumer)

Guess you like