for循環、並行流、串行流效率比較

User類

import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

@Builder
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    int id;
    String name;
    int sex;
    int age;

}

測試類

import org.springframework.web.bind.annotation.RestController;


import java.time.LocalDateTime;
import java.time.temporal.TemporalField;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

@RestController
public class TestController {

    public static void main(String[] args) {
        List<User> userList = new ArrayList<>();
        for (int i = 0; i < 100; i++) {
            int sex = 0;
            if ((i & 1) == 1) {
                sex = 1;
            }
            User user = User.builder().id(i).name("劉-" + i).sex(sex).age(i).build();
            userList.add(user);
        }
        System.out.println("=====數據總量：" + userList.size());

        long beginTime = System.currentTimeMillis();
        int sumAge1 = 0;
        for (User user : userList) {
            sumAge1 += user.getAge();
        }
        long endTime = System.currentTimeMillis();
        System.out.println("=====增強for循環所用時間 " + (endTime - beginTime) + " 毫秒" + " ，計算結果" + sumAge1);

        beginTime = System.currentTimeMillis();
        int sumAge2 = userList.stream().collect(Collectors.summingInt(User::getAge));
        endTime = System.currentTimeMillis();
        System.out.println("=====順序流所用時間 " + (endTime - beginTime) + " 毫秒， 計算結果" + sumAge2);


        beginTime = System.currentTimeMillis();
        int sumAge = userList.parallelStream().mapToInt(User::getAge).sum();
        endTime = System.currentTimeMillis();
        System.out.println("=====並行流所用時間 " + (endTime - beginTime) + " 毫秒， 計算結果" + sumAge);


    }

}

測試結果：

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

一千五百萬的時候並行流最快

 

到20000000就內存溢出了。

所以通常的處理邏輯for循環性能更優。