1. Streams filter() and collect()

package com.mkyong.java8;

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

2. Streams filter(), findAny() and orElse()

package com.mkyong.java8;

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

2.3 For multiple condition.

NowJava8.java

package com.mkyong.java8;

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()

.filter((p) -> "jack".equals(p.getName()) && 20 == p.getAge())

.findAny()

.orElse(null);

System.out.println("result 1 :" + result1);

//or like this

Person result2 = persons.stream()

.filter(p -> {

if ("jack".equals(p.getName()) && 20 == p.getAge()) {

return true;

}

return false;

}).findAny()

.orElse(null);

System.out.println("result 2 :" + result2);

}

}

Output

result 1 :Person{name='jack', age=20}

result 2 :Person{name='jack', age=20}

3. Streams filter() and map()

NowJava8.java

package com.mkyong.java8;

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

源文

https://www.mkyong.com/java8/java-8-streams-filter-examples/