[英]How to sort a collection using Collection.sort()
I am writing a program that stores an ArrayList
of Person
objects (input is from a text file). 我正在编写一个存储
Person
对象ArrayList
的程序(输入来自文本文件)。
This is the code for the Person
class, which I will create Person
objects from: 这是
Person
类的代码,我将根据以下代码创建Person
对象:
import java.io.Serializable;
public class Person implements Comparable<Person>, Serializable
{
private String firstName;
private String lastName;
private int age;
public Person(String firstName, String lastName, int age)
{
this.firstName = firstName;
this.lastName = lastName.toUpperCase();
this.age = age;
}
public int getAge()
{
return age;
}
public String getName()
{
return firstName;
}
/**
* @return a String of the details of a person in the format:
* Name: <firstName> <lastName> Age: <age>
*/
public String toString()
{
return
"Name: " + firstName + "" + lastName + "\t\t" + "Age: " + age;
}
/**
* Compare the age of the current instance of Person to another age of the specified Person
* @return negative number this < p
* @return 0 if this == p
* @return positive number if this > p
*/
public int compareTo(Person p) {
return ((Integer)this.getAge()).compareTo(p.getAge());
}
And I created a Comparable
interface: 我创建了一个
Comparable
接口:
public interface Comparable<T> {
public int compareTo(T o);
}
And here is the code for the class called Collection
which will create an ArrayList
to store Person
objects, I ommitted parts of the code that were not relevant as it is long: 以下是名为
Collection
的类的代码,该代码将创建一个ArrayList
来存储Person
对象,我忽略了很长的代码中不相关的部分:
import java.io.*;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.StringTokenizer;
import java.util.Iterator;
public class Collection
{
private ArrayList<Person> people;
public Collection()
{
people = new ArrayList<Person>();
}
public void readFromFile(String filename)
{
// code that will get input to assign values to fields to a Person
Person newPerson = new Person(firstNameToken, lastNameToken, ageToken);
}
/**
* Prints the details of each person held in the people ArrayList
*/
public void printDetails()
{
Iterator<Person> it = people.iterator();
while(it.hasNext())
{
Person p = it.next();
System.out.println(p.toString());
}
}
public static void main(String [] args) throws FileNotFoundException
{
Collection c = new Collection();
// check
//for(Person person : c.people)
//{
// System.out.println(person);
//}
Collections.sort(c.people);
}
}
However I get this error, the sort does not work: 但是我收到此错误,排序不起作用:
Exception in thread "main" java.lang.Error: Unresolved compilation problem: Bound mismatch: The generic method sort(List) of type Collections is not applicable for the arguments (ArrayList).
线程“主”中的异常java.lang.Error:未解决的编译问题:绑定不匹配:Collections类型的通用方法sort(List)不适用于参数(ArrayList)。 The inferred type Person is not a valid substitute for the bounded parameter >
推断的类型Person不是有效替代边界参数>
Does anyone know why? 有人知道为什么吗? I am looking furiously around on google for solutions, I can't see what I am missing.
我在google上四处寻找解决方案,我看不到我所缺少的东西。 I've implemented comparable..
我已经实现了可比性。
And I created a Comparable interface: public interface Comparable { public int compareTo(T o);
我创建了一个Comparable接口:public interface Comparable {public int compareTo(T o); }
}
You are not supposed to create your own interface. 您不应该创建自己的界面。 Use
java.lang.Comparable<T>
, the one that the Collections.sort()
method expects your object to implement 使用
java.lang.Comparable<T>
,它是Collections.sort()
方法期望您的对象实现的对象
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