Java8排序stream.sorted()

短命女 2021-12-18 06:04 209阅读 0赞

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][http_www.concretepage.com_java_jdk-8_java-8-stream-sorted-example]

[http_www.concretepage.com_java_jdk-8_java-8-stream-sorted-example]: http://www.concretepage.com/java/jdk-8/java-8-stream-sorted-example