Comparator comparingLong() method in Java with examples - GeeksforGeeks

29 Apr, 2019
The comparingLong(java.util.function.ToLongFunction) method of Comparator Interface in Java accepts a function as parameter that extracts an long sort key from a type T, and returns a Comparator that compares by that sort key.The returned comparator is serializable if the specified function is also serializable.
Syntax:
static <T> Comparator<T> 
    comparingLong(ToLongFunction <T> keyExtractor)

Parameters: This method accepts a single parameter keyExtractor which is the function used to extract the long sort key.
Return value: This method returns a comparator that compares by an extracted key
Exception: This method throws NullPolongerException if the argument is null.
Below programs illustrate comparingLong(java.util.function.ToLongFunction) method:Program 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 + "]";    }}
The output printed on console of IDE is shown below.Output:
Program 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;    }}
The output printed on console is shown below.Output:
References: https://docs.oracle.com/javase/10/docs/api/java/util/Comparator.html#comparingLong(java.util.function.ToLongFunction)
Java - util package
Java-Comparator
Java-Functions
Java
Java
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