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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