The comparingDouble(java.util.function.ToDoubleFunction) method of Comparator Interface in Java accepts a function as parameter that extracts an double 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> comparingDouble( ToDoubleFunction <T> keyExtractor)
Parameters: This method accepts a single parameter keyExtractor which is the function used to extract the double 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 comparingDouble(java.util.function.ToDoubleFunction) method:
Program 1:
// Java program to demonstrate Comparator // comparingDouble(ToDoubleFunction) 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" , 3500.56 );
User u2 = new User( "Joyita" , 4222.99 );
User u3 = new User( "Suvam" , 2832.34 );
User u4 = new User( "mahafuj" , 2522.76 );
// 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.comparingDouble(User::getSalary));
System.out.println( "\nAfterSort:" );
list.forEach(user -> System.out.println(user));
}
} class User implements Comparable<User> {
public String name;
public double salary;
public User(String name, double d)
{
this .name = name;
this .salary = d;
}
public int compareTo(User u1)
{
return name.compareTo(u1.name);
}
public String getName()
{
return name;
}
public void setName(String name)
{
this .name = name;
}
public double getSalary()
{
return salary;
}
public void setSalary( double salary)
{
this .salary = salary;
}
@Override
public String toString()
{
return "User [name=" + name
+ ", salary="
+ salary + "]" ;
}
} |
The output printed on console of IDE is shown below.
Output:
Program 2:
// Java program to demonstrate Comparator // comparingDouble(ToDoubleFunction) 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" , 32684.82 ),
new Order( "Vvekhfbkje2" , 28348.47 ),
new Order( "efkhfbekjfbe" , 47674.49 ),
new Order( "bhdhdfaddvad" , 78449.43 ),
new Order( "abkasbcjabjc" , 10104.43 ));
System.out.println( "Before Sort:" );
list.forEach(order -> System.out.println(order));
Collections.sort(list,
Comparator.comparingDouble(Order::getValue));
System.out.println( "\nAfter Sort:" );
list.forEach(order -> System.out.println(order));
}
} class Order implements Comparable<Order> {
public String orderNo;
public double value;
public int compareTo(Order o1)
{
return orderNo.compareTo(o1.orderNo);
}
public Order(String orderNo, double 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 double getValue()
{
return value;
}
public void setValue( double value)
{
this .value = value;
}
} |
The output printed on console is shown below.
Output: