31、Arrays数组排序（续）——自定义排序

　　自定义的类要按照一定的方式进行排序，比如一个Person类要按照年龄进行从小到大排序，比如一个Student类要按照成绩进行由高到低排序。

　　这里我们采用两种方式，一种是使用Comparable接口：让待排序对象所在的类实现Comparable接口，并重写Comparable接口中的compareTo()方法，缺点是只能按照一种规则排序。

　　另一种方式是使用Comparator接口：编写多个排序方式类实现Comparator接口，并重写新Comparator接口中的compare()方法，在调用Arrays的sort()时将排序类对象作为参数传入：public static void sort(T[] a,Comparatorc),根据指定比较器产生的顺序对指定对象数组进行排序。数组中的所有元素都必须是通过指定比较器可相互比较的(也就是说，对于数组中的任何 e1 和 e2 元素而言，c.compare(e1, e2) 不得抛出 ClassCastException)。优点是可以按照多种方式排序，你要按照什么方式排序，就创建一个实现Comparator接口的排序方式类，然后将该排序类的对象传入到Arrays.sort(待排序对象，该排序方式类的对象)

方式一：Comparable

 　　

import java.util.Arrays;


public class Hello {
    public static void main(String[] args) {
        Person p1=new Person("p1",25);
        Person p2=new Person("p2",23);
        Person p3=new Person("p3",27);
        Person p4=new Person("p4",32);
        Person p5=new Person("p5",18);
        
        Person[] arr=new Person[]{p1,p2,p3,p4,p5};
        System.out.println(Arrays.toString(arr));
        Arrays.sort(arr);
        System.out.println(Arrays.toString(arr));
    }
}
class Person implements Comparable<Person>{
    private String name;
    private int age;
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    @Override
    public int compareTo(Person o) {
        return age-o.age;
    }
    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + "]";
    }
}

输出结果：

[Person [name=p1, age=25], Person [name=p2, age=23], Person [name=p3, age=27], Person [name=p4, age=32], Person [name=p5, age=18]]
[Person [name=p5, age=18], Person [name=p2, age=23], Person [name=p1, age=25], Person [name=p3, age=27], Person [name=p4, age=32]]

方式二：Comparator

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


public class Hello {
    public static void main(String[] args) {
        Student s1=new Student("s1", 23, 89);
        Student s2=new Student("s2", 33, 68);
        Student s3=new Student("s3", 31, 75);
        Student s4=new Student("s4", 17, 80);
        Student[] arr=new Student[]{s1,s2,s3,s4};
        
        System.out.println("未排序:"+Arrays.toString(arr));
        Arrays.sort(arr, new SortByAge());
        System.out.println("按年龄排序:"+Arrays.toString(arr));
        Arrays.sort(arr, new SortByScore());
        System.out.println("按分数排序:"+Arrays.toString(arr));
    }
}
class Student {
    private String name;
    private int age;
    private double score;
    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 getScore() {
        return score;
    }
    public void setScore(double score) {
        this.score = score;
    }
    public Student(String name, int age, double score) {
        super();
        this.name = name;
        this.age = age;
        this.score = score;
    }
    @Override
    public String toString() {
        return "[name=" + name + ", age=" + age + ", score=" + score
                + "]";
    }
    
}

class SortByAge implements Comparator<Student>{

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

class SortByScore implements Comparator<Student>{

    @Override
    public int compare(Student o1, Student o2) {
        // TODO Auto-generated method stub
        return  o1.getScore()-o2.getScore()>0?1:-1;
    }
}

输出结果：

未排序:[[name=s1, age=23, score=89.0], [name=s2, age=33, score=68.0], [name=s3, age=31, score=75.0], [name=s4, age=17, score=80.0]]
按年龄排序:[[name=s4, age=17, score=80.0], [name=s1, age=23, score=89.0], [name=s3, age=31, score=75.0], [name=s2, age=33, score=68.0]]
按分数排序:[[name=s2, age=33, score=68.0], [name=s3, age=31, score=75.0], [name=s4, age=17, score=80.0], [name=s1, age=23, score=89.0]]

对于临时使用的可以使用匿名类的方式：（按年龄降序排序）

Arrays.sort(arr,new Comparator<Student>(){
    @Override
    public int compare(Student o1, Student o2) {
        // TODO Auto-generated method stub
        return o2.getAge()-o1.getAge();
    }    
});