Java Comparator thenComparingLong()方法及示例

Java中比较器接口的 thenComparingLong( java.util.function.ToLongFunction ) 方法返回一个具有提取Long排序键的函数的词表顺序比较器。

语法

default Comparator <T> thenComparingLong(
    ToLongFunction <T> keyExtractor)

参数： 该方法接受 keyExtractor ，它是用来提取Long sort key的函数。

返回值： 该方法返回一个由this和Long sort key组成的lexicographic-order比较器。

异常： 如果参数为空，该方法会抛出NullPointerException。

下面的程序说明了thenComparingLong(java.util.function.ToLongFunction)方法：
程序1 :

// Java program to demonstrate Comparator
// thenComparingLong(ToLongFunction) method
  
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
  
public class GFG {
    public static void main(String... args)
    {
        List<Users> list = createUsers();
        System.out.printf("before sort: %s%n", list);
        Collections.sort(list,
                         Comparator
                             .comparing(Users::getDepartment)
                             .thenComparingLong(Users::getId));
        System.out.printf("after sort: %s%n", list);
    }
  
    private static List<Users> createUsers()
    {
        return Arrays.asList(
            new Users(12311, "ME"),
            new Users(10211, "CSE"),
            new Users(33111, "CSE"),
            new Users(21000, "IT"),
            new Users(12133, "IT"),
            new Users(21445, "CSE"));
    }
  
    private static class Users {
        private long id;
        private String department;
  
        public Users(long id, String department)
        {
            this.id = id;
            this.department = department;
        }
  
        public long getId()
        {
            return id;
        }
  
        public void setId(long id)
        {
            this.id = id;
        }
  
        public String getDepartment()
        {
            return department;
        }
  
        public void setDepartment(String department)
        {
            this.department = department;
        }
  
        @Override
        public String toString()
        {
            return department + " - " + id;
        }
    }
}

输出：
Java中的比较器thenComparingLong方法及示例
你可以看到在这个例子中，首先按部门进行排序，如果部门相同，则按ID进行排序。

程序2 :

// Java program to demonstrate Comparator
// thenComparingLong(ToLongFunction) method
  
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
  
public class GFG {
    public static void main(String... args)
    {
  
        List<String> list
            = Arrays.asList("KKR", "CSK",
                            "MI", "KXIP", "RCB",
                            "SRH", "DC", "RR");
  
        try {
  
            // apply thenComparingLong
            Comparator.comparing(list::get)
                .thenComparingLong(null);
        }
        catch (Exception e) {
  
            System.out.printf("Exception:" + e);
        }
    }
}

打印在控制台的输出如下。
输出：
Java中的比较器thenComparingLong方法及示例