java 函數式編程

 

 

比較金典的例子：

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.experimental.Accessors;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;

public class CompletableFutureMallDemo {

    static List<NetMall> list= Arrays.asList(
            new NetMall("jd"),
            new NetMall("dangdang"),
            new NetMall("taobao")
    );

    public static List<String> getPrice(List<NetMall> list,String productName){
        return list.stream().map(
                netMall -> String.format(productName + " in %s price is %.2f", netMall.getNetMallName(),
                        netMall.calcPrice(productName)))
                .collect(Collectors.toList());
    }

    public static  List<String> getPriceByCompletableFuture(List<NetMall> list,String productName){
        return list.stream().map(netMall ->
                        CompletableFuture.supplyAsync(() ->
                String.format(productName + " in %s price is %.2f", netMall.getNetMallName(),
                        netMall.calcPrice(productName))
        )).collect(Collectors.toList())
                .stream().map(s -> s.join()).collect(Collectors.toList());
    }

    public static void main(String[] args) {
        long starTime=System.currentTimeMillis();
       List<String> list1= getPrice(list,"mysql");
       for (String element:list1){
           System.out.println(element);
       }
        long endTime=System.currentTimeMillis();
        System.out.println("-------------costTime:"+(endTime-starTime)+"毫秒");

        System.out.println("-----------------");

        long starTime1=System.currentTimeMillis();
        List<String> list2= getPriceByCompletableFuture(list,"mysql");
        for (String element:list2){
            System.out.println(element);
        }
        long endTime1=System.currentTimeMillis();
        System.out.println("-------------costTime:"+(endTime1-starTime1)+"毫秒");
    }

}

class NetMall{
    @Getter
    private String netMallName;

    public NetMall(String netMallName) {
        this.netMallName = netMallName;
    }

    public double calcPrice(String productName){
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
       return ThreadLocalRandom.current().nextDouble()*2+productName.charAt(0);
    }
}

@AllArgsConstructor
@NoArgsConstructor
@Data
@Accessors(chain = true)
class Student{
    private Integer id;
    private String studentName;
    private String major;
}