Java 8 中的 monadic 编程是否更慢？下面是我的测试(使用右偏 Either 为每个计算创建新实例)。命令式版本快 1000 倍。如何在获得可比性能的同时在 Java8 中进行 monadicaly 编程？

主.java

public class Main {

    public static void main(String args[]){
        Main m = new Main();
        m.work();
        m.work2();
    }


    public void work(){
        final long start = System.nanoTime();
        final Either<Throwable,Integer> result =
                Try(this::getInput).flatMap((s) ->
                Try(this::getInput).flatMap((s2) ->
                parseInt(s).flatMap((i) ->
                parseInt(s2).map((i2) ->
                i + i2
                ))));
        final long end = System.nanoTime();
        result.map(this::println).leftMap(this::println);
        System.out.println((end-start)/1000+"us to execute");
    }

    public void work2(){
        Object result;
        final long start = System.nanoTime();
        try {
            final String s = getInput();
            final String s2 = getInput();

            final int i = parzeInt(s);
            final int i2 = parzeInt(s2);
            result = i + i2;
        }catch(Throwable t){
            result=t;
        }
        final long end = System.nanoTime();
        println(result);
        System.out.println((end-start)/1000+"us to execute");
    }

    public <A> A println(final A a){
        System.out.println(a);
        return a;
    }

    public  String getInput(){
        final Integer value = new Random().nextInt();
        if(value % 2 == 0) return "Surprise!!!";
        return value+"";
    }

    public Either<Throwable,Integer> parseInt(final String s){
        try{
            return Either.right(Integer.parseInt(s));
        }catch(final Throwable t){
            return Either.left(t);
        }
    }

    public Integer parzeInt(final String s){
        return Integer.parseInt(s);
    }
}

Either.java

public abstract class Either<L,R>
{
    public static <L,R> Either<L,R> left(final L l){
        return new Left(l);
    }

    public static <L,R> Either<L,R> right(final R r){
        return new Right(r);
    }

    public static<L,R> Either<L,R> toEither(final Optional<R> oR,final L l){
        return oR.isPresent() ? right(oR.get()) : left(l);
    }

    public static <R> Either<Throwable,R> Try(final Supplier<R> sr){
        try{
            return right(sr.get());
        }catch(Throwable t){
            return left(t);
        }
    }

    public abstract <R2> Either<L,R2> flatMap(final Function<R,Either<L,R2>> f);

    public abstract  <R2> Either<L,R2> map(final Function<R,R2> f);

    public abstract  <L2> Either<L2,R> leftMap(final Function<L,L2> f);

    public abstract  Either<R,L> swap();

    public static class Left<L,R> extends Either<L,R> {
        final L l;

        private Left(final L l){
            this.l=l;
        }

        public <R2> Either<L,R2> flatMap(final Function<R,Either<L,R2>> f){
            return (Either<L,R2>)this;
        }

        public <R2> Either<L,R2> map(final Function<R,R2> f){
            return (Either<L,R2>)this;
        }

        public <L2> Either<L2,R> leftMap(final Function<L,L2> f){
            return new Left(f.apply(l));
        }

        public Either<R,L> swap(){
            return new Right(l);
        }
    }

    public static class Right<L,R> extends Either<L,R> {
        final R r;

        private Right(final R r){
            this.r=r;
        }

        public <R2> Either<L,R2> flatMap(final Function<R,Either<L,R2>> f){
            return f.apply(r);
        }

        public <R2> Either<L,R2> map(final Function<R,R2> f){
            return new Right(f.apply(r));
        }

        public <L2> Either<L2,R> leftMap(final Function<L,L2> f){
            return (Either<L2,R>)this;
        }

        public Either<R,L> swap(){
            return new Left(r);
        }
    }
}

最佳答案

虽然我不太理解你的努力——显然你正在使用 map 来产生副作用，而且你真的没有任何替代方法来从 Either 类型中拆箱结果——我已经测量过你在 JMH 上的工作是这样的。您对 Random 的用法有误，我已更正。这是我使用的代码:

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@OperationsPerInvocation(Measure.SIZE)
@Warmup(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
@State(Scope.Thread)
@Fork(1)
public class Measure
{
  static final int SIZE = 1;

  @Benchmark public Either<Throwable, Integer> workMonadically() {
    final Either<Throwable,Integer> result =
        Try(this::getInput).flatMap((s) ->
            Try(this::getInput).flatMap((s2) ->
                parseInt(s).flatMap((i) ->
                    parseInt(s2).map((i2) ->
                            i + i2
                    ))));
    return result;
  }

  @Benchmark public Object workImperatively() {
    Object result;
    try {
      final String s = getInput();
      final String s2 = getInput();

      final int i = parzeInt(s);
      final int i2 = parzeInt(s2);
      result = i + i2;
    }catch(Throwable t){
      result=t;
    }
    return result;
  }

  public String getInput() {
    final Integer value = ThreadLocalRandom.current().nextInt();
    if (value % 2 == 0) return "Surprise!!!";
    return String.valueOf(value);
  }

  public Either<Throwable,Integer> parseInt(final String s){
    try{
      return Either.right(Integer.parseInt(s));
    }catch(final Throwable t){
      return Either.left(t);
    }
  }

  public Integer parzeInt(final String s){
    return Integer.parseInt(s);
  }

  public static abstract class Either<L,R>
  {
    public static <L,R> Either<L,R> left(final L l){
      return new Left<>(l);
    }

    public static <L,R> Either<L,R> right(final R r){
      return new Right<>(r);
    }

    public static<L,R> Either<L,R> toEither(final Optional<R> oR,final L l){
      return oR.isPresent() ? right(oR.get()) : left(l);
    }

    public static <R> Either<Throwable,R> Try(final Supplier<R> sr){
      try{
        return right(sr.get());
      }catch(Throwable t){
        return left(t);
      }
    }

    public abstract <R2> Either<L,R2> flatMap(final Function<R,Either<L,R2>> f);

    public abstract  <R2> Either<L,R2> map(final Function<R,R2> f);

    public abstract  <L2> Either<L2,R> leftMap(final Function<L,L2> f);

    public abstract  Either<R,L> swap();

    public static class Left<L,R> extends Either<L,R> {
      final L l;

      private Left(final L l){
        this.l=l;
      }

      @Override public <R2> Either<L,R2> flatMap(final Function<R,Either<L,R2>> f){
        return (Either<L,R2>)this;
      }

      @Override public <R2> Either<L,R2> map(final Function<R,R2> f){
        return (Either<L,R2>)this;
      }

      @Override public <L2> Either<L2,R> leftMap(final Function<L,L2> f){
        return new Left<>(f.apply(l));
      }

      @Override public Either<R,L> swap(){
        return new Right<>(l);
      }
    }

    public static class Right<L,R> extends Either<L,R> {
      final R r;

      private Right(final R r){
        this.r=r;
      }

      @Override public <R2> Either<L,R2> flatMap(final Function<R,Either<L,R2>> f){
        return f.apply(r);
      }

      @Override public <R2> Either<L,R2> map(final Function<R,R2> f){
        return new Right<>(f.apply(r));
      }

      @Override public <L2> Either<L2,R> leftMap(final Function<L,L2> f){
        return (Either<L2,R>)this;
      }

      @Override public Either<R,L> swap(){
        return new Left<>(r);
      }
    }
  }
}

这是结果:

Benchmark                 Mode  Cnt     Score     Error  Units
Measure.workImperatively  avgt    5  1646,874 ± 137,326  ns/op
Measure.workMonadically   avgt    5  1990,668 ± 281,646  ns/op

所以几乎没有区别。

关于java - 如何在获得可比性能的同时在 Java8 中进行 monadicaly 编程？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29019165/