Java Comparator comparingLong()方法及示例

Java Comparator comparingLong()方法及示例

Java 中比较器接口的 comparingLong( java.util.function.ToLongFunction ) 方法接受一个函数作为参数,该函数从一个类型 T 中提取一个长排序键,并返回一个通过该排序键进行比较的比较器。如果指定的函数也是可序列化的,则返回的比较器是可序列化的。

语法

static <T> Comparator<T> 
    comparingLong(ToLongFunction <T> keyExtractor)
Java

参数: 该方法接受一个单参数 keyExtractor ,它是用于提取长排序键的函数。

返回值: 该方法返回一个比较器,通过提取的键进行比较。

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

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

程序1 :

// 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<User> 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<User> {
    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 + "]";
    }
}
Java

打印在IDE控制台的输出如下。

输出:

Java中的比较器comparingLong方法及示例

程序2 :

// 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<Order> 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<Order> {
    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;
    }
}
Java

打印在控制台的输出如下。

输出:

Java中的比较器comparingLong方法及示例

**参考文献: ** https://docs.oracle.com/javase/10/docs/api/java/util/Comparator.html#comparingLong(java.util.function.ToLongFunction)

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