Java中Comparable和Comparator

 public interface Comparable<T> {
    public int compareTo(T o);
}

public interface Comparator<T> {
    int compare(T o1, T o2);
    boolean equals(Object obj);
}

public class TestCompareComparatorAndComparable {
    private static class Student implements Comparable<Student> {
        private int  age;
        private String grade;
        public Student(int age, String grade) {
            this.age = age;
            this.grade = grade;
        }
        public int getAge() {
            return age;
        }
        public void setAge(int age) {
            this.age = age;
        }
        public String toString(){
            return age + "-" + grade;
        }
        public boolean euuals(Student student) {
            if(this.age == student.age && this.grade == student.grade) {
                return true;
            }
            return false;
        }
        @Override
        public int compareTo(Student student) {
            return this.grade.compareTo(student.grade);
        }
    }
    //定义一个关于Student类的比较器
    private static class StudentComparetorasc implements Comparator<Student> {
        @Override
        public int compare(Student o1, Student o2) {
            return (o1.getAge() - o2.getAge());
        }
    }
    //定义一个降序比较器
    private static class StudentComparetordesc implements Comparator<Student> {
        @Override
        public int compare(Student o1, Student o2) {
            return (o2.getAge() - o1.getAge());
        }
    }
    public static void main(String[] args) {
        // 新建ArrayList(动态数组)
        ArrayList<Student> list = new ArrayList<>();
        // 添加对象到ArrayList中
        list.add(new Student(8,"grade2"));
        list.add(new Student(7,"grade1"));
        list.add(new Student(10,"grade4"));
        list.add(new Student(9,"grade3"));
        // 打印list的原始序列
        System.out.printf("Original sort, list:%s\n", list);
        // 对list进行排序
        // 这里会根据“student实现的Comparable<String>接口”进行排序，即会根据“grade”进行排序
        Collections.sort(list);
        System.out.printf("Grade sort, list:%s\n", list);
        // 通过“比较器(AscAgeComparator)”，对list进行排序
        // AscAgeComparator的排序方式是：根据“age”的升序排序
        Collections.sort(list, new StudentComparetorasc());
        System.out.printf("asc (age)  sort, list:%s\n", list);
        // 通过“比较器(DescAgeComparator)”，对list进行排序
        // DescAgeComparator的排序方式是：根据“age”的降序排序
        Collections.sort(list, new StudentComparetordesc());
        System.out.printf("Desc(age) sort, list:%s\n", list);
        // 判断两个person是否相等
        testEquals();
    }
    /**
     * @desc 测试两个Person比较是否相等。
     *   由于Person实现了equals()函数：若两person的age、name都相等，则认为这两个person相等。
     *   所以，这里的p1和p2相等
     */
    private static void testEquals() {
        Student p1 = new Student(10, "grade1");
        Student p2 = new Student(11, "grade2");
        if (p1.equals(p2)) {
            System.out.printf("%s EQUAL %s\n", p1, p2);
        } else {
            System.out.printf("%s NOT EQUAL %s\n", p1, p2);
        }
    }
}
 

 @SuppressWarnings("unchecked")
    public static <T extends Comparable<? super T>> void sort(List<T> list) {
        list.sort(null);
    }
    @SuppressWarnings({"unchecked", "rawtypes"})
    public static <T> void sort(List<T> list, Comparator<? super T> c) {
        list.sort(c);
    }

@SuppressWarnings({"unchecked", "rawtypes"})
default void sort(Comparator<? super E> c) {
        Object[] a = this.toArray();
        Arrays.sort(a, (Comparator) c);
        ListIterator<E> i = this.listIterator();
        for (Object e : a) {
            i.next();
            i.set((E) e);
        }
 }