Java8排序stream.sorted()的使用

在这个页面上我们将提供java 8 Stream sorted（）示例。我们可以按照自然排序以及Comparator提供的排序对流进行排序。在java 8中Comparator可以使用lambda表达式进行实例化。我们还可以反转自然排序以及提供的排序Comparator。自然排序使用提供的顺序Comparable，必须由其实例是流元素的类实现。在这个页面上我们将排序List，Map并Set使用java 8流sorted()方法。

1.sorted()方法的语法示例。

1.1sorted()：它使用自然顺序对流的元素进行排序。元素类必须实现Comparable接口。

按自然升序对集合进行排序

list.stream().sorted() .stream().sorted();

自然序降序使用Comparator提供reverseOrder()方法

list.stream().sorted(Comparator.reverseOrder()) .stream().sorted(Comparator.reverseOrder());

1.2 sorted(Comparator<? super T> comparator):这里我们创建一个Comparator使用lambda表达式的实例。我们可以按升序和降序对流元素进行排序。

使用Comparator来对列表进行自定义升序。

list.stream().sorted(Comparator.comparing(Student::getAge)) .stream().sorted(Comparator.comparing(Student::getAge));

使用Comparator提供reversed()方法来对列表进行自定义降序。 。

list.stream().sorted(Comparator.comparing(Student::getAge).reversed()) .stream().sorted(Comparator.comparing(Student::getAge).reversed());

2.使用List流排序（）

package com.stream.demo;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class StreamListDemo {
 public static void main(String[] args) {
 List<Student> list = new ArrayList<>();
 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()));
 }
}

package com.stream.demo;

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;
 }
}

执行结果

---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

3.使用set流排序

package com.stream.demo;

import java.util.Comparator;
import java.util.HashSet;
import java.util.Set;

public class StreamSetDemo {
 public static void main(String[] args) {
 Set<Student> set = new HashSet<>();
 set.add(new Student(1, "Mahesh", 12));
 set.add(new Student(2, "Suresh", 15));
 set.add(new Student(3, "Nilesh", 10));

 System.out.println("---Natural Sorting by Name---");
 System.out.println("---Natural Sorting by Name---");
 set.stream().sorted().forEach(e -> System.out.println("Id:"
   + e.getId() + ", Name: " + e.getName() + ", Age:" + e.getAge()));

 System.out.println("---Natural Sorting by Name in reverse order---");
 set.stream().sorted(Comparator.reverseOrder()).forEach(e -> System.out.println("Id:"
   + e.getId() + ", Name: " + e.getName() + ", Age:" + e.getAge()));

 System.out.println("---Sorting using Comparator by Age---");
 set.stream().sorted(Comparator.comparing(Student::getAge))
   .forEach(e -> System.out.println("Id:" + e.getId() + ", Name: " + e.getName() + ", Age:" + e.getAge()));

 System.out.println("---Sorting using Comparator by Age in reverse order---");
 set.stream().sorted(Comparator.comparing(Student::getAge).reversed())
   .forEach(e -> System.out.println("Id:" + e.getId() + ", Name: " + e.getName() + ", Age:" + e.getAge()));
 }
}

4.使用Map流排序

package com.stream.demo;

import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;

public class StreamMapDemo {
 public static void main(String[] args) {
 Map<Integer, String> map = new HashMap<>();
 map.put(15, "Mahesh");
 map.put(10, "Suresh");
 map.put(30, "Nilesh");

 System.out.println("---Sort by Map Value---");
 map.entrySet().stream().sorted(Comparator.comparing(Map.Entry::getValue))
   .forEach(e -> System.out.println("Key: "+ e.getKey() +", Value: "+ e.getValue()));

 System.out.println("---Sort by Map Key---");System.out.println("---Sort by Map Key---");
 map.entrySet().stream().sorted(Comparator.comparing(Map.Entry::getKey))
   .forEach(e -> System.out.println("Key: "+ e.getKey() +", Value: "+ e.getValue()));
 }
}

这是在英文网站看到的示例，觉得还不错就翻译过来了。

原文链接：http://www.concretepage.com/java/jdk-8/java-8-stream-sorted-example

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