package n;public interface Comparable<Student> {?? public int compareTo(Student s);}package n;import java.util.Set;import java.util.TreeSet;public class Student implements Comparable<Student> {?????? int id;?????? String name;?????? public Student(int id, String name){?? ??? ??? this.id = id;?? ??? ??? this.name = name;?????? }?????? public int compareTo(Student s){?? ??? ??? if(this.id < s.id) return -1;?? ??? ??? else if(this.id > s.id) return 1;?? ??? ??? else return 0;?????? }?????? public String toString(){?? ??? ??? return "<" + this.id + "." + this.name + ">";?????? }?? ?public static void main(String[] args) {?? ??? ?// TODO 自動(dòng)生成的方法存根??????? Student[] stud = new Student[]{?????? ??? ??? ?new Student(1002, "張三"),?????? ??? ??? ?new Student(1003, "李四"),?????? ??? ??? ?new Student(1001, "王五")??????? };??????? Set<Student> ts = new TreeSet<Student>();??????? for(int i = 0; i < stud.length; i ++)?????? ??? ?ts.add(stud[i]);??????????? System.out.println(ts);?? ?}?? }
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念瑤Exception in thread "main" java.lang.ClassCastException: n.Student cannot be cast to java.lang.Comparable at java.util.TreeMap.compare(TreeMap.java:1188) at java.util.TreeMap.put(TreeMap.java:531) at java.util.TreeSet.add(TreeSet.java:255) at n.Student.main(Student.java:30)
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