TreeMap添加元素时异常 Comparable异常

package com.swift;import java.util.Comparator;import java.util.HashMap;import java.util.Iterator;import java.util.Map;import java.util.Map.Entry;import java.util.Set;import java.util.TreeMap;public class Map_keySet_entrySet {    public static void main(String[] args) {        /*         * TreeMap 集合存储自定义对象，并使用 2 中方式遍历获取         */                Map<Person,String> hm = new HashMap<Person, String>();        hm.put(new Person("lisi",18), "加拿大");        hm.put(new Person("zhangsa",17), "澳大利亚");        hm.put(new Person("zhangsa",17), "澳大利亚");        hm.put(new Person("wangwu",20), "新加坡");        hm.put(new Person("zhaoliu",19), "新西兰");        hm.put(new Person("zhaoliu",19), "新西兰");        hm.put(new Person("lisa",22), "迪拜");                //使用TreeMap无法排序比较是会出现Comparable错误 这时需要自己弄比较器        Map<Person,String> tree = new TreeMap<Person, String>(new Comparator<Person>() {            @Override            public int compare(Person arg0, Person arg1) {                int num=arg0.getAge()-arg1.getAge();                return num==0?arg0.getName().compareTo(arg1.getName()):num;            }                    });        tree.put(new Person("lisisi",18), "china");                //keySet方法一        Set<Person> set=hm.keySet();        for(Person per:set) {            System.out.println("人员："+per.toString()+"来自："+hm.get(per));        }                Set<Person> set1=tree.keySet();        for(Person per:set1) {            System.out.println("人员："+per.toString()+"来自："+tree.get(per));        }                //entrySet方法二        for(Map.Entry<Person, String> en:hm.entrySet()) {            System.out.println();            System.out.println("人员："+en.getKey().toString()+"来自："+en.getValue());        }                        Map<Person,String> tree1 = new TreeMap<Person, String>(new Comparator<Person>() {            @Override            public int compare(Person arg0, Person arg1) {                int num=arg0.getAge()-arg1.getAge();                return num==0?arg0.getName().compareTo(arg1.getName()):num;            }                    });        tree1.put(new Person("fengqichanglin",18), "langyabang");        System.out.println();        Iterator<?> it=tree1.entrySet().iterator();        while(it.hasNext()) {            Entry<Person,String> entry=(Entry<Person, String>) it.next();            System.out.println(entry.getKey().toString()+entry.getValue());        }                    }}

就会犯错误，就会有无数次让自己跌倒的机会出现，