java比较之Comparable和Comparator

介绍

Comparable和Comparator都是java的接口，Comparable在java.lang包下，而Comparator在java.util包下，两者功能都是排序。

1.Comparable

Comparable可以认为是一种内部比较器，我们在类定义时实现Comparable接口，并重写其compareTo方法，其返回类型为int
代码测试如下：

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

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

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

    @Override
    public int compareTo(Student o) {
        if(this.age>o.age){
            return 1;
        }else if(this.age == o.age){
            return 0;
        }else{
            return -1;
        }
    }
}

public class Test {
    public static void main(String[] args) {
        Student[] students = new Student[3];
        students[0] = new Student(18,"ahuang",88.3);
        students[1] = new Student(19,"dabai",87.3);
        students[2] = new Student(17,"zizi",89.3);

        Arrays.sort(students);

        System.out.println(Arrays.toString(students));
    }
}

//输出结果 
//[Student{age=17, name='zizi', score=89.3}, Student{age=18, name='ahuang', score=88.3}, Student{age=19, name='dabai', score=87.3}]

2.Comparator

Comparator是专门定义一个类比较器是实现的接口，需要重写其compare方法，其返回值为int、
代码测试如下：

class AgeComparator implements Comparator<Student>{
    @Override
    public int compare(Student o1,Student o2){
        return o1.age- o2.age;
    }
}

class StringComparator implements Comparator<Student>{
    @Override
    public int compare(Student o1,Student o2){
        return o1.name.compareTo(o2.name);
    }
}

class ScoreComparator implements Comparator<Student>{
    @Override
    public int compare(Student o1,Student o2){
        return (int)(o1.score- o2.score);
    }
}
public class Test2 {
    public static void main(String[] args) {
        Student[] students = new Student[3];
        students[0] = new Student(18,"ahuang",88.3);
        students[1] = new Student(19,"dabai",87.3);
        students[2] = new Student(17,"zizi",89.3);
        AgeComparator ageComparator = new AgeComparator();
        Arrays.sort(students,ageComparator);
        System.out.println(Arrays.toString(students));
        
        StringComparator stringComparator = new StringComparator();
        Arrays.sort(students,stringComparator);
        System.out.println(Arrays.toString(students));
    }
}
//输出结果
//[Student{age=17, name='zizi', score=89.3}, Student{age=18, name='ahuang', score=88.3}, Student{age=19, name='dabai', score=87.3}]
//[Student{age=18, name='ahuang', score=88.3}, Student{age=19, name='dabai', score=87.3}, Student{age=17, name='zizi', score=89.3}]

总结

1.Comparable在java.lang包下，Comparator在java.util包下
2.实现Comparable接口要重写comparTo方法，实现Comparator接口要重写compar方法
3.Comparable要修改原来的类实体，所以Comparator用得更多一些