Comparator.reverseOrder
是 Java 8 中引入的一种静态方法,它返回 Comparator
以对对象集合的反向自然排序进行排序。对于自然排序,一个类需要实现 Comparable
并定义 compareTo
方法。对象集合按照自然顺序按照 compareTo
进行排序。 Comparator.reverseOrder
颠倒了自然顺序。它在内部调用 Collections.reverseOrder()
并返回 Comparator
实例。查找 Comparator.reverseOrder
的 Java 源代码。
public static <T extends Comparable<? super T>> Comparator<T> reverseOrder() {
return Collections.reverseOrder();
}
Comparator
还提供了一种方法,如 Comparator.naturalOrder
,它对对象集合施加自然排序。数字的自然顺序是数字顺序,字符串按照字母顺序排序,日期按照时间顺序排序。 Java 类(如 Integer
、String
和 Date
)实现了 Comparable
并覆盖其 compareTo
方法以实现自然排序。为了方便我们的类中的自然排序,我们需要实现 Comparable
接口并定义 compareTo
方法。Comparator.reverseOrder
返回 Comparator
以反转自然顺序。我们可以将 Comparator.reverseOrder
与 Stream.sorted
、List.sort
、Collections.sort
和 Arrays.sort
一起使用,以逆自然顺序对对象集合进行排序。
Stream.sorted
返回一个由该流的元素组成的流,根据提供的比较器进行排序。
StreamSortedDemo.java
package com.concretepage;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
public class StreamSortedDemo {
public static void main(String[] args) {
List<Integer> numList = Arrays.asList(12, 10, 15, 8, 11);
numList.stream().sorted(Comparator.reverseOrder()).forEach(n -> System.out.print(n + " "));
System.out.println("\n-----------");
List<String> strList = Arrays.asList("Varanasi", "Allahabad", "Kanpur", "Noida");
strList.stream().sorted(Comparator.reverseOrder()).forEach(s -> System.out.print(s + " "));
System.out.println("\n-----------");
List<Student> stdList = Student.getStudentList();
stdList.stream().sorted(Comparator.reverseOrder()).forEach(s -> System.out.print(s.getName() + " "));
}
}
Student.java
package com.concretepage;
import java.util.Arrays;
import java.util.List;
public class Student implements Comparable<Student> {
private String name;
private int age;
public Student(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
@Override
public int compareTo(Student s) {
return name.compareTo(s.getName());
}
public static List<Student> getStudentList() {
Student s1 = new Student("Ram", 18);
Student s2 = new Student("Shyam", 22);
Student s3 = new Student("Mohan", 19);
Student s4 = new Student("Mahesh", 20);
Student s5 = new Student("Krishna", 21);
List<Student> list = Arrays.asList(s1, s2, s3, s4, s5);
return list;
}
}
输出
15 12 11 10 8
-----------
Varanasi Noida Kanpur Allahabad
-----------
Shyam Ram Mohan Mahesh Krishna
Collections.sort
根据给定的 Comparator 实例对指定列表进行排序。
CollectionsSortDemo.java
package com.concretepage;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class CollectionsSortDemo {
public static void main(String[] args) {
List<Integer> numList = Arrays.asList(12, 10, 15, 8, 11);
Collections.sort(numList, Comparator.reverseOrder());
numList.forEach(n -> System.out.print(n + " "));
System.out.println("\n-----------");
List<String> strList = Arrays.asList("Varanasi", "Allahabad", "Kanpur", "Noida");
Collections.sort(strList, Comparator.reverseOrder());
strList.forEach(s -> System.out.print(s + " "));
System.out.println("\n-----------");
List<Student> stdList = Student.getStudentList();
Collections.sort(stdList, Comparator.reverseOrder());
stdList.forEach(s -> System.out.print(s.getName() + " "));
}
}
List.sort
根据给定的 Comparator 实例对该列表进行排序。
ListSortDemo.java
package com.concretepage;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
public class ListSortDemo {
public static void main(String[] args) {
List<Integer> numList = Arrays.asList(12, 10, 15, 8, 11);
numList.sort(Comparator.reverseOrder());
numList.forEach(n -> System.out.print(n + " "));
System.out.println("\n-----------");
List<String> strList = Arrays.asList("Varanasi", "Allahabad", "Kanpur", "Noida");
strList.sort(Comparator.reverseOrder());
strList.forEach(s -> System.out.print(s + " "));
System.out.println("\n-----------");
List<Student> stdList = Student.getStudentList();
stdList.sort(Comparator.reverseOrder());
stdList.forEach(s -> System.out.print(s.getName() + " "));
}
}
Arrays.sort
根据指定比较器的顺序对指定的对象数组进行排序。
ArraysSortDemo.java
package com.concretepage;
import java.util.Arrays;
import java.util.Comparator;
public class ArraysSortDemo {
public static void main(String[] args) {
Student s1 = new Student("Ram", 18);
Student s2 = new Student("Shyam", 22);
Student s3 = new Student("Mohan", 19);
Student[] stdArray = { s1, s2, s3 };
Arrays.sort(stdArray, Comparator.reverseOrder());
for (Student s : stdArray) {
System.out.print(s.getName() + " ");
}
}
}
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