Question

java collections.sort

import java.util.*;
public class Listtest{
public static void main(String args[]){
List l1 = new LinkedList();
l1.add(new name("ac","A"));
l1.add(new name("uang","u"));
name n = new name("ad","A");
//int x = n.compareTo(new name("a2","B"));
l1.add(new name("at","t"));
l1.add(new name("louis","uang"));
l1.add(new name("guanshi","yang"));
Collections.sort(l1);
System.out.println(l1);
//System.out.println(x);
}
}

class name{
private String firstname;
private String lastname;
public name(String firstname,String lastname){
this.firstname = firstname ;
this.lastname = lastname;
}

public String getfirstname(){
return firstname;
}

public String getlastname(){
return lastname;
}

public String toString(){
return firstname + " " + lastname;
}

public void setfirstname(String firstname){
this.firstname = firstname ;
}

public void setlastname(String lastname){
this.lastname = lastname ;
}

public boolean equals(Object obj){
boolean ben = false;
if(obj instanceof name){
name name = (name)obj;
if(this.lastname == name.lastname){
ben = true;
ben = ben?this.firstname==name.firstname:false;
return ben;
}
}
return super.equals(obj);
}

public int hashCode(){
String str = new String(lastname);
return str.hashCode();
}

int compareTo(name o){
name name = (name)o ;
int k = lastname.compareTo(name.lastname);
return (k != 0? k : firstname.compareTo(name.firstname));
}
}
程序运行报错：不可比较的错误。不知道问题出在哪里

Answer 1

Collections的sort(List)方法要求参数必须实现Comparable接口
你的name类没有实现，所以不能运行
这样改class name implements Comparable {
然后把最后一个
int compareTo(name o){
name name = (name)o ;
int k = lastname.compareTo(name.lastname);
return (k != 0? k : firstname.compareTo(name.firstname));
}
改成
public int compareTo(Object o){
然后在函数里面把o转换成name类型的

Answer 2

int compareTo(name o){

我记得应该是Object o