Comparator comparingInt() in Java with examples

The comparingInt(java.util.function.ToIntFunction) method accepts a function as parameter that extracts an int 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> comparingInt(ToIntFunction <T> keyExtractor)

Parameters: This method accepts a single parameter keyExtractor which is the function used to extract the integer sort key.

Return value: This method returns a comparator that compares by an extracted key

Exception: This method throws NullPointerException if the argument is null.



Below programs illustrate comparingInt(java.util.function.ToIntFunction) method:
Program 1:

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// Java program to demonstrate
// Comparator.comparingInt(java.util.function.ToIntFunction)  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", 25);
        User u2 = new User("Joyita", 22);
        User u3 = new User("Suvam", 28);
        User u4 = new User("mahafuj", 25);
  
        // before sort
        List<User> list
            = Arrays.asList(u2, u1, u4, u3);
        System.out.println("Before Sort:");
        list.forEach(User
                     -> System.out.println("User age "
                                           + User.getAge()));
  
        Collections.sort(list,
                         Comparator.comparingInt(
                             User::getAge));
        System.out.println("\nAfterSort:");
        list.forEach(User
                     -> System.out.println("User age "
                                           + User.getAge()));
    }
}
class User implements Comparable<User> {
    public String name;
    public int age;
  
    public User(String name, int age)
    {
        this.name = name;
        this.age = age;
    }
  
    public int compareTo(User u1)
    {
        return name.compareTo(u1.name);
    }
  
    public String getName()
    {
        return name;
    }
  
    public void setName(String name)
    {
        this.name = name;
    }
  
    public int getAge()
    {
        return age;
    }
  
    public void setAge(int age)
    {
        this.age = age;
    }
  
    @Override
    public String toString()
    {
        return "User [name=" + name
            + ", age=" + age + "]";
    }
}

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The output printed on console of IDE is shown below.
Output:

Program 2:

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// Java program to demonstrate
// Comparator.comparingInt(java.util.function.ToIntFunction)  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", 320),
            new Order("Vvekhfbkje2", 242),
            new Order("efkhfbekjfbe", 1345),
            new Order("bhdhdfaddvad", 230),
            new Order("abkasbcjabjc", 100));
        System.out.println("Before Sort:");
        list.forEach(order -> System.out.println(order));
  
        Collections.sort(list,
                         Comparator.comparingInt(
                             Order::getValue));
        System.out.println("\nAfter Sort:");
        list.forEach(order -> System.out.println(order));
    }
}
class Order implements Comparable<Order> {
    public String orderNo;
    public int value;
  
    public int compareTo(Order o1)
    {
        return orderNo.compareTo(o1.orderNo);
    }
  
    public Order(String orderNo, int 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 int getValue()
    {
        return value;
    }
  
    public void setValue(int value)
    {
        this.value = value;
    }
}

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The output printed on console is shown below.
Output:

References: https://docs.oracle.com/javase/10/docs/api/java/util/Comparator.html#comparingInt(java.util.function.ToIntFunction)

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