比较器

package com.cisco.www.sort;

import java.util.Arrays;
import java.util.PriorityQueue;
import java.util.TreeMap;
import java.util.TreeSet;

/**
 * 比较器：负数第一个参数放前面，正数第二个参数放前面，相等则二者是相等的
 */
public class Comparator {
    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;
        }
    }
    public static class IdAscendingComparator implements java.util.Comparator<Student>{

        @Override
        public int compare(Student o1, Student o2) {
            //返回负数，则前面的值更小(按照升序)，否则后面的值小(按照降序)。

            return o1.id-o2.id;
        }
    }
    //比较器：负数第一个参数放前面，正数第二个参数放前面，相等则二者是相等的
    public static class IdDescendingComparator implements java.util.Comparator<Student>{

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




    public static class AgeAscendingComparator implements java.util.Comparator<Student>{

        @Override
        public int compare(Student o1, Student o2) {
            //返回负数，则前面的值更小(按照升序)，否则后面的值小(按照降序)。

            return o1.age-o2.age;
        }
    }
    //比较器：负数第一个参数放前面，正数第二个参数放前面，相等则二者是相等的
    public static class AgeDescendingComparator implements java.util.Comparator<Student>{

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

    public static class MyComp implements java.util.Comparator<Integer>{

        @Override
        public int compare(Integer o1, Integer o2) {
            return o2 - o1;
        }
    }
    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);
        //创建Student数组，将student都放进去
        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);

        Integer[] arr= {3,2,4,1,0};
        Arrays.sort(arr,new MyComp());
        printArray(arr);

        //优先级队列就是堆,如果什么参数都不提供，那么默认按照内存地址来组织这个堆
        PriorityQueue<Student> heap = new PriorityQueue<>(new IdAscendingComparator());
        heap.add(student3);
        heap.add(student2);
        heap.add(student1);

        while (!heap.isEmpty()){
            //每次弹出堆的堆顶，然后将堆的大小减1
            Student student = heap.poll();
            System.out.println("Name:"+student.name+",Id:"+student.id+",Age:"+student.age);
        }

        //红黑树
        TreeSet<Student> treeSet = new TreeSet<>(new IdAscendingComparator());
        //...........


    }
    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 printArray(Integer[] arr){
        if(arr==null){
            return;
        }
        for(int i= 0 ; i<arr.length;i++){
            System.out.print(arr[i]+" ");
        }
        System.out.println();
    }

}