Comparator comparingDouble() method in Java with examples - GeeksforGeeks

29 Apr, 2019
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:
References: https://docs.oracle.com/javase/10/docs/api/java/util/Comparator.html#comparingDouble(java.util.function.ToDoubleFunction)
Java - util package
Java-Comparator
Java-Functions
Java
Java
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