Java中的Comparable接口和Comparator接口核心机制详解

import java.util.Arrays;
//类实现接口，使其具备比较的功能
class Student implements Comparable<Student>{
    private String name;
    private int age;
    public Student(String name,int age){
        this.name = name;
        this.age = age;
    }
    public int getAge() {
        return age;
    }
    public String getName(){
        return name;
    }
    //年龄排序
    public int compareTo(Student o){
//        return this.age - o.age;
        return Integer.compare(this.age,o.age);
    }
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}
public class Test01 {
    public static void main(String[] args) {
        //按照年龄从小到大排序
        Student[] students = new Student[]{
                new Student("xiaoming", 19),
                new Student("xiaohong",20),
                new Student("xiaohua",15),
                new Student("xiaoshuai",24),
        };
        System.out.println("排序前"+ Arrays.toString(students));
        //Arrays.sort()能够根据我们定义的 compareTo方法排序
        Arrays.sort(students);  
        System.out.println("排序后" + Arrays.toString(students));
            //两个对象进行比较
//        Student student1 = new Student("小明",28);
//        Student student2 = new Student("小红",19);
//        System.out.println(student1.compareTo(student2));    //输出9
//        <0 则s1<s2 =0则s1=s2 >0则s1>s2
}

//姓名排序
   public int compareTo(Student o){
       return this.name.compareTo(o.name);//在String中已经实现了compareTo方法，这里可直接调用
   }

import java.util.Arrays;
import java.util.Comparator;
class Teacher{
    private String name;
    private int age;
    public Teacher(String name,int age){
        this.name = name;
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public int getAge() {
        return age;
    }
    @Override
    public String toString() {
        return "Teacher{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}
public class Test02 {
    public static void main(String[] args) {
        Teacher[] teachers = new Teacher[]{
                new Teacher("Zhang",33),
                new Teacher("Li",40),
                new Teacher("Hen",28),
                new Teacher("Tang",18)
        };
        //按照年龄大小比较
        AgeComparator ageComparator = new AgeComparator();
        System.out.println("排序前" + Arrays.toString(teachers));
        Arrays.sort(teachers,ageComparator);    //将实例化的比较器作为参数传入sort
        System.out.println("按年龄排序后" + Arrays.toString(teachers));
        //按照姓名长度比较
        NameLenComparator nameLenComparator = new NameLenComparator();
        Arrays.sort(teachers,nameLenComparator);    //将实例化的比较器作为参数传入sort
        System.out.println("按姓名长度排序后" + Arrays.toString(teachers));
    }
    //(静态内部类)自定义年龄比较器
    static class AgeComparator implements Comparator<Teacher>{
        public int compare(Teacher o1,Teacher o2){
            return o1.getAge()- o2.getAge();
        }
    }
    //(静态内部类)自定义姓名长度比较器
    static class NameLenComparator implements Comparator<Teacher>{
        public int compare(Teacher o1,Teacher o2){
            return o1.getName().length() - o2.getName().length();
        }
    }
}

// 使用Lambda表达式替代完整的比较器类
        // 按年龄排序
        Arrays.sort(teachers, (t1, t2) -> t1.getAge() - t2.getAge());
        System.out.println("按年龄排序后: " + Arrays.toString(teachers));
        // 按姓名长度排序
        Arrays.sort(teachers, (t1, t2) -> t1.getName().length() - t2.getName().length());
        System.out.println("按姓名长度排序后: " + Arrays.toString(teachers));
        // 甚至可以更复杂：先按年龄，年龄相同按姓名长度
        Arrays.sort(teachers, (t1, t2) -> {
            int ageCompare = t1.getAge() - t2.getAge();
            if (ageCompare != 0) {
                return ageCompare;
            }
            return t1.getName().length() - t2.getName().length();
        });
        System.out.println("按年龄和姓名长度排序后: " + Arrays.toString(teachers));
    }

// 按年龄排序
Arrays.sort(teachers, (t1, t2) -> t1.getAge() - t2.getAge());

// 先按年龄，年龄相同按姓名长度
Arrays.sort(teachers, (t1, t2) -> {
    int ageCompare = t1.getAge() - t2.getAge();
    if (ageCompare != 0) {
        return ageCompare;
    }
    return t1.getName().length() - t2.getName().length();
});