Java8排序stream.sorted()

       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