一文搞懂Comparable和Comparator

相同点

• 都是用来比较两个对象“顺序”的接口

不同点

• Comparable在java.lang包下，Comparator在java.util包下
• Comparable是在集合内部元素中定义的方法实现的排序，Comparator是在集合外部实现的排序，是策略模式。

具体实现

Comparable需要集合中存放的对象实现Comparable接口，重写comparaTo()方法

以Student类倒序排序举例：

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

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

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

    @Override
    public int compareTo(Student s) {
        if(this.age-s.age>0) return -1;
        if(this.age-s.age<0) return 1;
        else return 0;
    }
}
class Test{
    public static void main(String[] args) {
        List list = new ArrayList<>();
        Student s1 = new Student(14,"lisi");
        Student s2 = new Student(34,"zhangsan");
        Student s3 = new Student(23,"wangwu");
        list.add(s1);
        list.add(s2);
        list.add(s3);
        Collections.sort(list);
        for(Student s : list){
            System.out.println(s);
        }

    }
}

 Comparator只需要在Collections.sort()中传入比较器，不需要改变元素类，符合OOP思想。在这里我们利用了Lambda表达式。

public class Student {
    public int age;
    public String name;

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

    @Override
    public String toString() {
        return "Student{" +
                "age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
}
class Test{
    public static void main(String[] args) {
        List list = new ArrayList<>();
        Student s1 = new Student(14,"lisi");
        Student s2 = new Student(34,"zhangsan");
        Student s3 = new Student(23,"wangwu");
        list.add(s1);
        list.add(s2);
        list.add(s3);
        Collections.sort(list,(o1,o2)->{
            if(o1.age-o2.age>0) return -1;
            if(o1.age-o2.age<0) return 1;
            else return 0;
        });
        for(Student s : list){
            System.out.println(s);
        }

    }
}