Java中的Comparator compareLong()方法和例子

Java 中 Comparator 接口的 comparisonLong( Java Java.ToLongFunction )方法接受一个函数作为参数，该函数从类型 T 中提取一个长排序键，并返回一个按该排序键进行比较的比较器。返回的比较器是可序列化的，如果指定的函数也是可序列化的。

句法：

static  Comparator 
    comparingLong(ToLongFunction  keyExtractor)

参数：此方法接受单个参数keyExtractor ，它是用于提取长排序键的函数。

返回值：此方法返回一个比较器，通过提取的键进行比较

异常：如果参数为 null，则此方法抛出 NullPolongerException。

下面的程序说明了 compareLong(Java 函数.ToLongFunction) 方法：
方案一：

// Java program to demonstrate Comparator
// comparingLong(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)
    {
  
        // create some user objects
        User u1 = new User("Aaman", 25724474);
        User u2 = new User("Joyita", 2262848);
        User u3 = new User("Suvam", 2824444);
        User u4 = new User("mahafuj", 2544244);
  
        // before sort
        List list = Arrays.asList(u2, u1, u4, u3);
        System.out.println("Before Sort:");
        list.forEach(user -> System.out.println(user));
  
        Collections.sort(list,
                         Comparator.comparingLong(
                             User::getregistrationId));
        System.out.println("\nAfterSort:");
        list.forEach(user -> System.out.println(user));
    }
}
  
class User implements Comparable {
    public String name;
    public long registrationId;
  
    public User(String name, long registrationId)
    {
        this.name = name;
        this.registrationId = registrationId;
    }
  
    public int compareTo(User u1)
    {
        return name.compareTo(u1.name);
    }
  
    public String getName()
    {
        return name;
    }
  
    public void setName(String name)
    {
        this.name = name;
    }
  
    public long getregistrationId()
    {
        return registrationId;
    }
  
    public void setregistrationId(long registrationId)
    {
        this.registrationId = registrationId;
    }
  
    @Override
    public String toString()
    {
        return "User [name=" + name
            + ", registrationId="
            + registrationId + "]";
    }
}

打印在 IDE 控制台上的输出如下所示。
输出：

方案二：

// Java program to demonstrate Comparator
// comparingLong(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)
    {
  
        // before sort
        List list = Arrays.asList(
            new Order("A382y482y48", 3204355),
            new Order("Vvekhfbkje2", 2425355),
            new Order("efkhfbekjfbe", 1345435),
            new Order("bhdhdfaddvad", 2305535),
            new Order("abkasbcjabjc", 1005454));
        System.out.println("Before Sort:");
        list.forEach(order -> System.out.println(order));
  
        Collections.sort(list,
                         Comparator.comparingLong(
                             Order::getValue));
        System.out.println("\nAfter Sort:");
        list.forEach(order -> System.out.println(order));
    }
}
  
class Order implements Comparable {
    public String orderNo;
    public long value;
  
    public int compareTo(Order o1)
    {
        return orderNo.compareTo(o1.orderNo);
    }
  
    public Order(String orderNo, long value)
    {
        super();
        this.orderNo = orderNo;
        this.value = value;
    }
  
    @Override
    public String toString()
    {
        return "Order [orderNo=" + orderNo
            + ", value=" + value + "]";
    }
  
    public String getOrderNo()
    {
        return orderNo;
    }
  
    public void setOrderNo(String orderNo)
    {
        this.orderNo = orderNo;
    }
  
    public long getValue()
    {
        return value;
    }
  
    public void setValue(long value)
    {
        this.value = value;
    }
}

控制台上打印的输出如下所示。
输出：

参考资料： https: Java Java 函数)