原文链接：http://www.concretepage.com/java/jdk-8/java-8-stream-sorted-example
国外对Java8一系列总结的不错， 翻译过来给大家共享
这篇文章将会讲解Java 8 Stream sorted()示例， 我们能够以自然序或着用Comparator 接口定义的排序规则来排序一个流。Comparator 能用用lambada表达式来初始化， 我们还能够逆序一个已经排序的流。
接下来我们将会使用java 8 的流式sorted排序List 、Map 、 Set
1、sorted() 默认使用自然序排序， 其中的元素必须实现Comparable 接口
2、sorted(Comparator<? super T> comparator) ：我们可以使用lambada 来创建一个Comparator 实例。可以按照升序或着降序来排序元素。
下面代码以自然序排序一个list
list.stream().sorted() 自然序逆序元素，使用Comparator 提供的reverseOrder() 方法
list.stream().sorted(Comparator.reverseOrder()) 使用Comparator 来排序一个list
list.stream().sorted(Comparator.comparing(Student::getAge)) 把上面的元素逆序
list.stream().sorted(Comparator.comparing(Student::getAge).reversed()) Stream sorted() with List
我们排序一组装着Student 类对象的List 集合。 首先我们使用自然序， 接着我们使用Comparator 分别进行升序和降序：
SortList.java
package com.concretepage; import java.util.ArrayList; import java.util.Comparator; import java.util.List; import java.util.stream.Collectors; public class SortList { public static void main(String[] args) { List<Student> list = new ArrayList<Student>(); list.add(new Student(1, "Mahesh", 12)); list.add(new Student(2, "Suresh", 15)); list.add(new Student(3, "Nilesh", 10)); System.out.println("---Natural Sorting by Name---"); List<Student> slist = list.stream().sorted().collect(Collectors.toList()); slist.forEach(e -> System.out.println("Id:"+ e.getId()+", Name: "+e.getName()+", Age:"+e.getAge())); System.out.println("---Natural Sorting by Name in reverse order---"); slist = list.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList()); slist.forEach(e -> System.out.println("Id:"+ e.getId()+", Name: "+e.getName()+", Age:"+e.getAge())); System.out.println("---Sorting using Comparator by Age---"); slist = list.stream().sorted(Comparator.comparing(Student::getAge)).collect(Collectors.toList()); slist.forEach(e -> System.out.println("Id:"+ e.getId()+", Name: "+e.getName()+", Age:"+e.getAge())); System.out.println("---Sorting using Comparator by Age with reverse order---"); slist = list.stream().sorted(Comparator.comparing(Student::getAge).reversed()).collect(Collectors.toList()); slist.forEach(e -> System.out.println("Id:"+ e.getId()+", Name: "+e.getName()+", Age:"+e.getAge())); } }
* Student.java *
package com.concretepage;
public class Student implements Comparable<Student> { private int id; private String name; private int age; public Student(int id, String name, int age) { this.id = id; this.name = name; this.age = age; } public int getId() { return id; } public String getName() { return name; } public int getAge() { return age; } @Override public int compareTo(Student ob) { return name.compareTo(ob.getName()); } @Override public boolean equals(final Object obj) { if (obj == null) { return false; } final Student std = (Student) obj; if (this == std) { return true; } else { return (this.name.equals(std.name) && (this.age == std.age)); } } @Override public int hashCode() { int hashno = 7; hashno = 13 * hashno + (name == null ? 0 : name.hashCode()); return hashno; } }
* Output *
---Natural Sorting by Name--- Id:1, Name: Mahesh, Age:12 Id:3, Name: Nilesh, Age:10 Id:2, Name: Suresh, Age:15 ---Natural Sorting by Name in reverse order--- Id:2, Name: Suresh, Age:15 Id:3, Name: Nilesh, Age:10 Id:1, Name: Mahesh, Age:12 ---Sorting using Comparator by Age--- Id:3, Name: Nilesh, Age:10 Id:1, Name: Mahesh, Age:12 Id:2, Name: Suresh, Age:15 ---Sorting using Comparator by Age with reverse order--- Id:2, Name: Suresh, Age:15 Id:1, Name: Mahesh, Age:12 Id:3, Name: Nilesh, Age:10