Java basics - the sorting method of the Arrays class

1. The sorting method of the Arrays class:

public static void sort(type[] a) //Sort the array in ascending order by default

public static <T> void sort(Type[] a, Comparator<?suprt T > c) //use comparator object to customize sorting

2. Custom sorting rules: Set the comparator object corresponding to the Comparator interface to formulate the comparison rules.

• If it is considered that the data on the left is greater than the data on the right, return a positive integer (return 1); 
• If the data on the left is considered to be smaller than the data on the right, return a negative integer (return -1); 
• If the data on the left is considered to be equal to the data on the right, return 0; 

return 1	exchange order
return -1	do not exchange order
return 0	do not exchange order

 3. Case study:

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

/**
 * Comparator比较对象
 */
public class ArraysDemo {
    public static void main(String[] args) {
        //1.Arrays的sort方法对于有值特性的数组是默认升序排序
        int[] ages = {34,12,42,23};
        Arrays.sort(ages);
        System.out.println(Arrays.toString(ages));

        //2.降序排序（自定义比较器对象，只支持引用类型的排序）
        Integer[] ages1 = {34,12,42,23};
        /*
        参数一：被排序的数组，必须是引用类型的元素
        参数二：匿名内部类对象，代表一个比较器对象
         */
        Arrays.sort(ages1, new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
//                return o1-o2;//默认升序
                return o2-o1;//默认降序-(o1-o2)
            }
        });
        System.out.println(Arrays.toString(ages1));

        System.out.println("-------------------------------");
        Student[] students = new Student[3];
        students[0]  = new Student("小花",23,157.5);
        students[1]  = new Student("小星",21,167.5);
        students[2]  = new Student("小清",20,177.5);
        System.out.println(Arrays.toString(students));
        
        //对int型的年龄排序
        Arrays.sort(students, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                return o1.getAge()-o2.getAge();//升序排序
            }
        });
        System.out.println(Arrays.toString(students));
        
        //对double型的身高排序
        Arrays.sort(students, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                return Double.compare(o1.getHeight(), o2.getHeight());
            }
        });
        System.out.println(Arrays.toString(students));

    }

}

class Student{
    private String name;
    private int age;
    private double height;

    public Student() {
    }

    public Student(String name, int age, double height) {
        this.name = name;
        this.age = age;
        this.height = height;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", height=" + height +
                '}';
    }
}