JDK 8 之 Stream sorted() 示例

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