java - 将对象添加到 ArrayList 中不会出现错误

Question

我只是想在 Eclipse 中向 ArrayList 添加一些对象，但在“persons.add(one);”下不断收到错误(语法错误，插入“... VariableDeclaratorId”以完成 FormalParameterList)。知道我做错了什么吗？

package thequestion;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

class PersonComparator implements Comparator<Person>{

   @Override
   public int compare(Person o1, Person o2) {
       return 0;
   }

   Person one = new Person("Kevin", "Gresmer");
   List<Person> persons = new ArrayList<Person>();

   persons.add(one);

   public void sortByLastName(List people) {
       Comparator comp = new PersonComparator();
       Collections.sort(people, comp);
   }
}


public class Person {
    private String firstName = null;
    private String lastName = null;

    public Person(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
}

Answer 1

persons.add(one) 行是一条语句，并且不能在代码块(方法、构造函数等)之外有语句。此外，您的 Comparator 应包含与您正在进行的比较相关的代码。我认为这不是存储列表或实现 sortByLastName() 方法的正确位置。