Java：如何對自定義類型ArrayList進行排序

Question

我有一個自定義類型Position(x,y,z) ，現在我創建一個ArrayList<Position> ，我想按z的值排序這個數組，從小到大，我怎么能用Collections.sort做到這一點還是有其他有效的分類方法？

當我嘗試使用時

public class PositionComparator implements Comparator<Position> {

        @Override
        public int compare(Position o1, Position o2) {
            // TODO Auto-generated method stub
            return o1.height().compareTo(o2.height());

        }

    }

得到一個錯誤

Cannot invoke compareTo(double) on the primitive type double

Answer 1

嘗試

Collections.sort(SortList, new Comparator<Position>(){
            public int compare(Position p1, Position p2) {
                return p1.z- p2.z;
            }
        });

Answer 2

Collections.sort  

例如

class User {

    String name;
    String age;

    public User(String name, String age) {
        this.name = name;
        this.age = age;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}
import java.util.Comparator;

public class ComparatorUser implements Comparator {

    public int compare(Object arg0, Object arg1) {
        User user0 = (User) arg0;
        User user1 = (User) arg1;

        int flag = user0.getAge().compareTo(user1.getAge());
        if (flag == 0) {
            return user0.getName().compareTo(user1.getName());
        } else {
            return flag;
        }
    }

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

public class SortTest {

    public static void main(String[] args) {
        List userlist = new ArrayList();
        userlist.add(new User("dd", "4"));
        userlist.add(new User("aa", "1"));
        userlist.add(new User("ee", "5"));
        userlist.add(new User("bb", "2"));
        userlist.add(new User("ff", "5"));
        userlist.add(new User("cc", "3"));
        userlist.add(new User("gg", "6"));

        ComparatorUser comparator = new ComparatorUser();
        Collections.sort(userlist, comparator);

        for (int i = 0; i < userlist.size(); i++) {
            User user_temp = (User) userlist.get(i);
            System.out.println(user_temp.getAge() + "," + user_temp.getName());
        }

    }
}

Answer 3

我使用這個（只是我剪切和過去但同樣的想法的一個例子）用於降序排序：

@Override
public int compare(Member m1, Member m2) {

    double fit1 = m1.getFitness() ;
    double fit2 = m2.getFitness() ;
    if (fit2>fit1)
            return 1;
    else if (fit2<fit1)
            return -1;
    else
            return  0;
}

Answer 4

您需要實現Comparator ，它將比較z屬性的值。