Java8

https://baijiahao.baidu.com/s?id=1711922146914662710&wfr=spider&for=pc

stream

https://blog.csdn.net/q1532440739/article/details/113864280

filter()和collect()

在Java 8中，stream.filter()过滤List列表，collect()将流转换为List列表

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class NowJava8 {
    public static void main(String[] args) {
        List<String> lines = Arrays.asList("spring", "node", "mkyong");
        List<String> result = lines.stream()                // convert list to stream
                .filter(line -> !"mkyong".equals(line))     // we dont like mkyong
                .collect(Collectors.toList());              // collect the output and convert streams to a List
        result.forEach(System.out::println);                //output : spring, node
    }
}
// output
spring
node

filter()、findAny()和orElse()

在java8中，stream.filter()过滤List列表，findAny()、orElse(null)返回满足条件的对象

public class Person {
    private String name;
    private int age;
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    //gettersm setters, toString
}

import java.util.Arrays;
import java.util.List;
public class NowJava8 {
    public static void main(String[] args) {
        List<Person> persons = Arrays.asList(
                new Person("mkyong", 30),
                new Person("jack", 20),
                new Person("lawrence", 40)
        );
        Person result1 = persons.stream()                        // Convert to steam
                .filter(x -> "jack".equals(x.getName()))        // we want "jack" only
                .findAny()                                      // If 'findAny' then return found
                .orElse(null);                                  // If not found, return null
        System.out.println(result1);
        Person result2 = persons.stream()
                .filter(x -> "ahmook".equals(x.getName()))
                .findAny()
                .orElse(null);
        System.out.println(result2);
    }
}
// output
Person{name='jack', age=20}
null

filter()和map()

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class NowJava8 {
    public static void main(String[] args) {
        List<Person> persons = Arrays.asList(
                new Person("mkyong", 30),
                new Person("jack", 20),
                new Person("lawrence", 40)
        );
        String name = persons.stream()
                .filter(x -> "jack".equals(x.getName()))
                .map(Person::getName)                        //convert stream to String
                .findAny()
                .orElse("");
        System.out.println("name : " + name);
        List<String> collect = persons.stream()
                .map(Person::getName)
                .collect(Collectors.toList());
        collect.forEach(System.out::println);
    }
}
//output
name : jack
mkyong
jack
lawrence