基于JDK8-lambda表达式四种forEach性能对比

package com.huajie.Lambda; 
import lombok.extern.slf4j.Slf4j;
import org.junit.Before;
import org.junit.Test;
import java.util.ArrayList;
import java.util.List;
 
@Slf4j
public class Mode2 {
    List<User> listUser = new ArrayList<>();
    @Before
    public void initList() {
        listUser = this.getListUsers();
    }
 
    @Test
    public void test() {
        //一般forEach
        long startSimpleTime = System.currentTimeMillis();
        for (User user : listUser) {
            user.toString();
        }
        long endSimpleTime = System.currentTimeMillis();
        System.out.println("Simple:" + (endSimpleTime - startSimpleTime));
 
        //java8中新的forEach
        long startLambda = System.currentTimeMillis();
        listUser.forEach(User::toString);
        long endLambda = System.currentTimeMillis();
        System.out.println("Lambda:" + (endLambda - startLambda));
 
        //java8中新的stream+forEach
        long startStream = System.currentTimeMillis();
        listUser.stream().forEach(User::toString);
        long endStream = System.currentTimeMillis();
        System.out.println("Stream:" + (endStream - startStream));
 
        //java8中新的parallelStream+forEach
        long startParallelStream = System.currentTimeMillis();
        listUser.parallelStream().forEach(User::toString);
        long endParallelStream = System.currentTimeMillis();
        System.out.println("ParallelStream:" + (endParallelStream - startParallelStream));
    }
 
    private List<User> getListUsers() {
        List<User> listUser = new ArrayList<User>();
        for (int i = 0; i < 10000000; i++) {
            listUser.add(new User("user" + i, i));
        }
        return listUser;
    }
}

package com.huajie.Lambda;
import lombok.Data;
@Data
public class User {
    private String name;
    private Integer age;
 
    public User(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
}

public static void testJDK8ForEach(){
  List<String> asList = Arrays.asList("a","b","a","d");
  int i=0;
  // jdk7 for
  for(String s:asList){
   if(s.equals("a")){
    ++i;
   }
  }
  //2  jdk8 forEach
  asList.forEach(s -> {
   if(s.equals("a")){
    ++i;  // Local variable i defined in an enclosing scope must be final or effectively final
   }
  });
  System.out.println(i);
  //3  jdk8 stream
  long count = asList.stream().filter(s -> s.equalsIgnoreCase("a")).count();
  System.out.println(count);
 }