Java中的比较器之Comparator.md

Java中的比较器之Comparator

目录

• Comparator的作用
• Comparator的使用

Comparator的作用

用于定义类的具体排序规则, 比如根据类的某个属性升序或降序排序

Comparator的使用

import java.util.Arrays;
import java.util.Comparator;

public class ComparatorDemo {
	public static class Student {
		public String name;
		public int id;
		public int age;

		public Student(String name, int id, int age) {
			this.name = name;
			this.id = id;
			this.age = age;
		}
	}
	
	// ID升序
	public static class IdAscendingComparator implements Comparator<Student> {

		@Override
		public int compare(Student o1, Student o2) {
			return o1.id - o2.id;
		}

	}

	// ID降序
	public static class IdDescendingComparator implements Comparator<Student> {

		@Override
		public int compare(Student o1, Student o2) {
			return o2.id - o1.id;
		}

	}

	// 年龄升序
	public static class AgeAscendingComparator implements Comparator<Student> {

		@Override
		public int compare(Student o1, Student o2) {
			return o1.age - o2.age;
		}

	}

	// 年龄降序
	public static class AgeDescendingComparator implements Comparator<Student> {

		@Override
		public int compare(Student o1, Student o2) {
			return o2.age - o1.age;
		}

	}

	public static void printStudents(Student[] students) {
		for (Student student : students) {
			System.out.println("Name : " + student.name + ", Id : " + student.id + ", Age : " + student.age);
		}
		System.out.println("===========================");
	}

	public static void main(String[] args) {
		Student student1 = new Student("A", 1, 23);
		Student student2 = new Student("B", 2, 21);
		Student student3 = new Student("C", 3, 22);

		Student[] students = new Student[] { student3, student2, student1 };
		printStudents(students);

		Arrays.sort(students, new IdAscendingComparator());
		printStudents(students);

		Arrays.sort(students, new IdDescendingComparator());
		printStudents(students);

		Arrays.sort(students, new AgeAscendingComparator());
		printStudents(students);

		Arrays.sort(students, new AgeDescendingComparator());
		printStudents(students);
	}
}