关于Java8 Lambda Expressions，市面已有比较丰富的学习案例，本文章纯粹为学习笔记，话不多说，直接上代码。
package com.jfpal.finance.prepo.lambda;
import java.util.*;
import java.util.function.Consumer;
import java.util.function.IntBinaryOperator;
import java.util.function.IntSupplier;
import java.util.function.Predicate;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toCollection;
import static java.util.stream.Collectors.toList;
/**
* Java8 Lambda Expressions学习案例
* @author Zack
* @version 1.0
* @date 2018/8/14
*/
public class LambdaTest {
public static void main(String[] args) {
testFunInterface();
testForEach();
testRunable();
testComparator();
testStream();
}
/**
* 常用的函数式接口
*/
private static void testFunInterface() {
System.out.println("---------------------------- cutting line---------------------------");
IntSupplier intSupplier = () -> 5;
System.out.println(intSupplier.getAsInt());
Consumer<String> stringConsumer = (String s) -> System.out.println(s);
stringConsumer.accept("test string");
IntBinaryOperator intBinaryOperator = (int x, int y) -> x + y;
System.out.println(intBinaryOperator.applyAsInt(10, 20));
}
/**
* 使用Lambda简化集合的操作
*/
private static void testForEach() {
System.out.println("---------------------------- cutting line---------------------------");
String[] atp = {"Jenk Cheng", "Rafael Nadal", "Novak Djokovic", "Stanislas Wawrinka", "David Ferrer"};
List<String> players = Arrays.asList(atp);
for (String player : players) {
System.out.print(player + "; ");
}
// Using lambda expression and functional operations
players.forEach((player) -> System.out.print(player + "; "));
// Using double colon operator in Java 8
players.forEach(System.out::println);
}
/**
* 使用Lambda简化线程的操作
*/
private static void testRunable() {
System.out.println("---------------------------- cutting line---------------------------");
// Using anonymous innerclass
new Thread(new Runnable() {
@Override
public void run() {
System.out.println("Hello world 1!");
}
}).start();
// Using lambda expression
new Thread(() -> System.out.println("Hello world 2!")).start();
// Using anonymous innerclass
Runnable race1 = new Runnable() {
@Override
public void run() {
System.out.println("Hello world 3!");
}
};
// Using lambda expression
Runnable race2 = () -> System.out.println("Hello world 4!");
// Run em!
race1.run();
race2.run();
}
/**
* 使用Lambda简化比较器的操作
*/
private static void testComparator(){
System.out.println("---------------------------- cutting line---------------------------");
String[] players = {"Jenk Cheng", "Rafael Nadal", "Novak Djokovic", "Stanislas Wawrinka", "David Ferrer", "Roger Federer", "Andy Murray", "Tomas Berdych", "Juan Martin Del Potro", "Richard Gasquet", "John Isner"};
// Sort players by name using anonymous innerclass
Arrays.sort(players, new Comparator<String>() {
@Override
public int compare(String s1, String s2) {
return (s1.compareTo(s2));
}
});
// Sort players by name using lambda expression
Comparator<String> sortByName = (String s1, String s2) -> (s1.compareTo(s2));
Arrays.sort(players, sortByName);
// or this
Arrays.sort(players, (String s1, String s2) -> (s1.compareTo(s2)));
}
/**
* java8流式操作集合、对象
* 支持快速排序、过滤、统计、并行处理等操作
*/
private static void testStream(){
System.out.println("---------------------------- cutting line---------------------------");
List<Person> javaProgrammers = new ArrayList<Person>() {
{
add(new Person("Maude", "Jaimie", "Java programmer", "female", 27, 1900));
add(new Person("Shawn", "Randall", "Java programmer", "male", 30, 2300));
add(new Person("Elsdon", "Jaycob", "Java programmer", "male", 43, 2000));
add(new Person("Tamsen", "Brittany", "Java programmer", "female", 23, 1500));
add(new Person("Floyd", "Donny", "Java programmer", "male", 33, 1800));
add(new Person("Sindy", "Jonie", "Java programmer", "female", 32, 1600));
add(new Person("Vere", "Hervey", "Java programmer", "male", 22, 1200));
add(new Person("Palmer", "Dene", "Java programmer", "male", 33, 2000));
add(new Person("Addison", "Pam", "Java programmer", "female", 34, 1300));
add(new Person("Jayden", "Corrina", "Java programmer", "female", 35, 1700));
}
};
List<Person> phpProgrammers = new ArrayList<Person>() {
{
add(new Person("Victor", "Channing", "PHP programmer", "male", 32, 1600));
add(new Person("Tori", "Sheryl", "PHP programmer", "female", 21, 1000));
add(new Person("Alvin", "Lance", "PHP programmer", "male", 38, 1600));
add(new Person("Osborne", "Shad", "PHP programmer", "male", 32, 1100));
add(new Person("Jarrod", "Pace", "PHP programmer", "male", 34, 1550));
add(new Person("Evonne", "Shari", "PHP programmer", "female", 40, 1800));
add(new Person("Clarette", "Cicely", "PHP programmer", "female", 23, 1200));
add(new Person("Rosalind", "Layla", "PHP programmer", "female", 25, 1300));
add(new Person("Fraser", "Hewie", "PHP programmer", "male", 36, 1100));
add(new Person("Quinn", "Tamara", "PHP programmer", "female", 21, 1000));
}
};
// Define some filters
Predicate<Person> ageFilter = (p) -> (p.getAge() > 25);
Predicate<Person> salaryFilter = (p) -> (p.getSalary() > 1400);
Predicate<Person> genderFilter = (p) -> ("female".equals(p.getGender()));
// Reuse filters
System.out.println("Show female Java programmers older than 24 years:");
javaProgrammers.stream()
.filter(ageFilter)
.filter(genderFilter)
.forEach((p) -> System.out.println(p.getFirstName() + "," + p.getLastName()));
System.out.println("Sort and show the first 5 Java programmers by name:");
List<Person> sortedJavaProgrammers = javaProgrammers
.stream()
.sorted((p, p2) -> (p.getFirstName().compareTo(p2.getFirstName())))
.limit(5)
.collect(toList());
sortedJavaProgrammers.forEach(System.out::println);
System.out.println("Sort and show Java programmers by salary:");
sortedJavaProgrammers = javaProgrammers
.stream()
.sorted((p, p2) -> (p.getSalary() - p2.getSalary()))
.collect(toList());
sortedJavaProgrammers.forEach(System.out::println);
System.out.println("Get PHP programmers first name to String:");
String phpDevelopers = phpProgrammers
.stream()
.map(Person::getFirstName)
.collect(joining(" ; "));
System.out.println(phpDevelopers);
System.out.println("Get Java programmers last name to TreeSet:");
TreeSet<String> javaDevLastName = javaProgrammers
.stream()
.map(Person::getLastName)
.collect(toCollection(TreeSet::new));
javaDevLastName.forEach(System.out::println);
System.out.println("Streams can also be parallel. An example is below:");
System.out.println("Calculate total money spent for paying Java programmers:");
int totalSalary = javaProgrammers
.parallelStream()
.mapToInt(p -> p.getSalary())
.peek(System.out::println)
.sum();
System.out.println("totalSalary:" + totalSalary);
System.out.println("Get count, min, max, sum, and average from person salary:");
IntSummaryStatistics stats = javaProgrammers
.parallelStream()
.mapToInt(p -> p.getSalary())
.summaryStatistics();
System.out.println("Max salary in stats : " + stats.getMax());
System.out.println("Lowest salary in stats : " + stats.getMin());
System.out.println("Sum of all numbers : " + stats.getSum());
System.out.println("Average of all numbers : " + stats.getAverage());
}
}
package com.jfpal.finance.prepo.lambda;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
/**
* @author Zack
* @version 1.0
* @date 2018/8/14
*/
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Person {
private String firstName;
private String lastName;
private String job;
private String gender;
private int salary;
private int age;
}
说明：以上测试案例均源于国外这篇文章，英语不错的可以点进去浏览。
http://www.jguru.com/article/core/start-using-java-lambda-expressions.html