勤怠学习会20230329 java stream api

Main.java

package org.winry;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.BenchmarkMode;
import org.openjdk.jmh.annotations.Mode;
import org.openjdk.jmh.runner.RunnerException;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.stream.IntStream;
import java.util.stream.Stream;

//@Fork(value = 1, warmups = 2)
@BenchmarkMode(Mode.AverageTime)
public class Main {

    private static final List<String> DATA = getData();

    public static void main(String[] args) throws RunnerException {
//        Options opt = new OptionsBuilder()
//                .include(Main.class.getSimpleName())
//                .build();
//        new Runner(opt).run();
        new Main().peek();
    }

    @Benchmark
    public List<Integer> filterMap() {
        return DATA.stream()
                .filter(s -> {
                    try {
                        Integer.parseInt(s);
                        return true;
                    } catch (NumberFormatException e) {
                        return false;
                    }
                })
                .map(Integer::parseInt).toList();
    }

    @Benchmark
    public List<Integer> flatMap() {
        return DATA.stream()
                .flatMap(s -> {
                    try {
                        return Stream.of(Integer.parseInt(s));
                    } catch (NumberFormatException e) {
                        return Stream.empty();
                    }
                }).toList();
    }

    @Benchmark
    public List<Integer> mapMulti() {
        return DATA.stream()
                .<Integer>mapMulti((s, consumer) -> {
                    try {
                        consumer.accept(Integer.parseInt(s));
                    } catch (NumberFormatException ignore) {
                    }
                }).toList();
    }

    @Benchmark
    public List<Integer> forLoop() {
        var list = new ArrayList<Integer>();
        for (var s : DATA) {
            try {
                list.add(Integer.parseInt(s));
            } catch (NumberFormatException ignore) {
            }
        }
        return list;
    }

    public void peek() {
        DATA.stream().peek(System.out::println).count();
    }

    public void forEach() {
        DATA.stream().forEach(System.out::println);
    }

    private static List<String> getData() {
        var random = new Random();
        return IntStream.range(0, 5_000_000)
                .mapToObj(i -> nextInt(random) ? String.valueOf(random.nextInt()) : "cant parse")
                .toList();
    }

    private static boolean nextInt(Random random) {
        return random.nextDouble() > 0.9;
    }
}