现在有一个自定义学生的学生类,里面有name属性,和age属性,我们如何去比较大小?

class Student{
    public String name;
    public int age;

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

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}
public class Test {
    public static void main(String[] args){
        Student student1 = new Student("zhangsan",18);
        Student student2 = new Student("lisi",20);
    }
}

自定义类型因为有很多的属性,编译器不知道怎么去比较大小,因此需要我们自定义比较规则.让他去具备可比较的功能 

方法1:实现Comparable接口,重写comparaeTo方法(自定义)

class Student implements Comparable<Student>{
    public String name;
    public int age;

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

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

    @Override
    public int compareTo(Student o) {
       return this.age-o.age;
    }
}
public class Test {
    public static void main(String[] args){
        Student student1 = new Student("zhangsan",18);
        Student student2 = new Student("lisi",20);
        if(student1.compareTo(student2)>0){
            System.out.println("student1 > student2");
        }else if(student1.compareTo(student2) == 0){
            System.out.println("student==student");
        }else{
            System.out.println("student1 < student2");
        }
    }
}

 如果需求更换,需要临时换一个比较规则,此时使用comparable就不好修改了

方法2:Comparator接口

我们可以写一个类,实现Comparator接口,重写compare接口,可以这个类(比较器)作为参数传递,相当于给一个类传递了比较规则

import java.util.Comparator;

class Student implements Comparable<Student>{
    public String name;
    public int age;

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

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

    @Override
    public int compareTo(Student o) {
       return this.age-o.age;
    }
}
class NameComparator implements Comparator<Student> {

    @Override
    public int compare(Student o1, Student o2) {
        return o1.name.compareTo(o2.name);
    }
}
public class Test {
    public static void main(String[] args){
        Student student1 = new Student("zhangsan",18);
        Student student2 = new Student("lisi",20);
        NameComparator nameComparator = new NameComparator();
        if(nameComparator.compare(student1,student2)>0){
            System.out.println("student1 > student2");
        }else if (nameComparator.compare(student1,student2)<0){
            System.out.println("student < student2");
        }else {
            System.out.println("student1 == student2");
        }
    }
}

 comparable和comparator接口返回值是 Int类型 可以比较大小,而equals方法返回类型是 boolean,
只能判断是否相等