如何将比较器添加到内部类？

Question

    public class Prerequisites {

        private class Course implements Comparator<Course> {
            public String name;
            public LinkedList<Course> requiredFor;
            public LinkedList<Course> prerequisites;

            Course(String name) {
                requiredFor = new LinkedList<Course>();
                prerequisites = new LinkedList<Course>();
                this.name = name;
            }

            @Override
            public int compare(Course c0, Course c1) {
                Pattern p = Pattern.compile("[A-Z]*");
                Matcher matcher0 = p.matcher(c0.name);
                Matcher matcher1 = p.matcher(c1.name);
                matcher0.find();
                matcher1.find();
                int courseNumber0 = Integer.parseInt(c0.name.substring(matcher0.end(),c0.name.length()));
                int courseNumber1 = Integer.parseInt(c1.name.substring(matcher1.end(),c1.name.length()));
                if(courseNumber0 > courseNumber1) {
                    return 1;
                }
                else if(courseNumber0 < courseNumber1) {
                    return -1;
                }
                else {
                    return matcher0.group().compareTo(matcher1.group());
                }
            }

            @Override
            public String toString(){
                return this.name;
            }
        }
    public void compare(String args[]) {
        Course c0 = new Course("CSE110");
        Course c1 = new Course("DSE110");
        LinkedList<Course> courses = new LinkedList<Course>();
        courses.add(c0);
        courses.add(c1);
        **Collections.sort(courses);** //gives compiler error

    }
 }

Why adding Collections.sort() for this inner class is not working ? I am not able to figure that out from the compiler error.

Answer 1

You probably meant to implement Comparable , not Comparator .

That's what the Collections#sort method expects :

public static <T extends Comparable<? super T>> void sort(List<T> list)

Answer 2

您应该实现Comparable而不是Comparator 。

Answer 3

Collections.sort(courses);

- If its the above, what you want to implement then its java.lang.Comparable Interface that you want to implement, and not java.util.Comparator Interface.

- Moreover Comparable Interface is used when you need to Sort the item on the basis of only one attribute.

But if you want to sort the items on the basis of more than one Attribute , then please implement java.util.Comparator Interface .

Collections.sort(List l, Comparator<T> t);