如何根据自定义订单指南订购对象列表？

Question

data class User(
    val name: String,
    val address: Address,
    val group: String
)

data class Address(
    val street: String,
    val city: String
)

我有一个用户列表。我需要按照 Kotlin（或 Java）中的指南按自定义顺序对这个列表进行排序。

1. 首先由

   group

   订购如下团购。 （不是字母顺序）
   • 数学
   • 科学
   • 英语
   • 底部的其他所有值无顺序

2. 然后按照以下城市顺序按

   city

   订购。 （排名不分先后）
   • 悉尼
   • 阿德莱德
   • 墨尔本
   • 底部的其他所有值无顺序

3. 然后按

   street

   逆序排列

4. 然后按

   name

   按字母顺序排列

如何按照上述指南编写比较器或自定义方法来订购列表？ 如果需要，

Address

班级可以进入

User

班级。

Answer 1

为此，您需要一个比较器，定义两个映射（groupOrder 和 cityOrder），将组和城市的名称映射到它们相应的订单号。

和其他人一样简单地实现 Comperator

val groupOrder = mapOf(
        "Maths" to 1,
        "Science" to 2,
        "English" to 3,
    )

    val cityOrder = mapOf(
        "Sydney" to 1,
        "Adelaide" to 2,
        "Melbourne" to 3,
    )

    val customComparator = Comparator<User> { u1, u2 ->
        // First, compare by group using the custom order
        val groupOrder1 = groupOrder[u1.group] ?: Int.MAX_VALUE
        val groupOrder2 = groupOrder[u2.group] ?: Int.MAX_VALUE
        if (groupOrder1 != groupOrder2) {
            groupOrder1.compareTo(groupOrder2)
        } else {
            // If groups are the same, compare by city using the custom order
            val cityOrder1 = cityOrder[u1.address.city] ?: Int.MAX_VALUE
            val cityOrder2 = cityOrder[u2.address.city] ?: Int.MAX_VALUE
            if (cityOrder1 != cityOrder2) {
                cityOrder1.compareTo(cityOrder2)
            } else {
                // If cities are the same, compare by street in reverse alphabetical order
                u2.address.street.compareTo(u1.address.street)
                    .takeIf { it != 0 }
                    ?: // If streets are the same, compare by name in alphabetical order
                    u1.name.compareTo(u2.name)
            }
        }
    }
 val userList = listOf(User("kari", Address("M5","Adelaide"), "Maths"),
    User("dari", Address("M6","Melbourne"),"English"))
 // Usage: sort the list of users using the custom comparator
val sortedList = userList.sortedWith(customComparator)

Answer 2

你需要像这样在类 User 中实现 Comparable

    class User
implements Comparable{
    String name;
    Address address;
    String group;
    Integer groupRank = Integer.valueOf(7);
    Integer addressRank = Integer.valueOf(7);
    public User(String name, Address address, String group)
    {
        this.name = name;
        this.address = address;
        this.group = group;
        if (group.equals("Maths"))groupRank = 1;
        if (group.equals("Science"))groupRank = 2;
        if (group.equals("English"))groupRank = 3;

        // this should be moved into the Address class
        if (address.city.equals("Sydney"))addressRank = 1;
        if (address.city.equals("Adelaide"))addressRank = 2;
        if (address.city.equals("Melbourne"))addressRank = 3;
    }

    public int compareTo(Object o) {
        // do something if o is not User
        User other = (User) o;
        int groupCompare = this.groupRank.compareTo(other.groupRank);
        
        // Address class should implement Comparable and have its own compreTo 
        if (groupCompare != 0)return groupCompare;
        else return this.addressRank.compareTo(other.addressRank);
    }
}
class Address{
    String city;
    String street;
}