java comparator 与comparable

今天重新看了一下java的TreeSet，教程里面讲解了，对于自定义的class，当构造TreeSet的时候，需要传递一个Comparator，以防止ClassCastException。但是这样做的话，每个class需要一个实现comparator的比较类，比较繁琐。还有一种方法，自定义的class实现comparable接口。先上代码，最后说不同。

1，实现comparator

 

class Teacher {
    private int age;

    Teacher(int age) {
        this.age = age;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Teacher:" + this.age;
    }
}

class TeacherComparator implements Comparator {
    @Override
    public int compare(Object o1, Object o2) {
        Teacher t1 = (Teacher) o1;
        Teacher t2 = (Teacher) o2;
        return t1.getAge() - t2.getAge();
    }
}

//main method
TreeSet set2 = new TreeSet(new TeacherComparator());
set2.add(new Teacher(10));
set2.add(new Teacher(50));
set2.add(new Teacher(70));
set2.add(new Teacher(20));
set2.add(new Teacher(160));

System.out.println(set2);
//out put
[Teacher:10, Teacher:20, Teacher:50, Teacher:70, Teacher:160]

 上面为新增一个比较器class

 

2

class Student implements Comparable {
    private int score;

    Student(int score) {
        this.score = score;
    }

    @Override
    public String toString() {
        return "Student:" + this.score;
    }

    @Override
    public int compareTo(Object o) {
        Student s = (Student) o;
        return -(this.getScore() - s.getScore());
    }

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }
}

//main
TreeSet set = new TreeSet();
Student s1 = new Student(10);
Student s2 = new Student(30);
Student s3 = new Student(20);
Student s4 = new Student(70);
Student s5 = new Student(50);
set.add(s1);
set.add(s2);
set.add(s3);
set.add(s4);
set.add(s5);
System.out.println(set);
//output
[Student:70, Student:50, Student:30, Student:20, Student:10]

实现了comparable接口。 

 

3.个人感觉实现comparable比较简单，实现起来不用新增一个class，不会那么繁琐。它们实现的接口不一样comparable实现comparaTo(Object o)接口，compartor实现compar(Object o1,Object o2)。