• 如果您觉得本站非常有看点,那么赶紧使用Ctrl+D 收藏吧

Java8排序stream.sorted()

java 来源:kris999 1次浏览

使用Java8排序stream.sorted()

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() 

1
自然序逆序元素,使用Comparator 提供的reverseOrder() 方法

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

1
使用Comparator 来排序一个list

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

1
把上面的元素逆序

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

1
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


版权声明:本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系管理员进行删除。
喜欢 (0)