The thenComparingDouble(java.util.function.ToDoubleFunction) method of Comparator Interface in Java returns a lexicographic-order comparator with a function that extracts a double sort key. This method is applied after comparing method if you want to apply another comparing for those values which are equal in the comparing method.
Syntax:
default Comparator <T> thenComparingDouble(
ToDoubleFunction <T> keyExtractor)
Parameters: This method accepts keyExtractor which is the function used to extract the Double sort key.
Return value: This method returns a lexicographic-order comparator composed of this and then the Double sort key.
Exception: This method throws NullPointerException if the argument is null.
Below programs illustrate thenComparingDouble(java.util.function.ToDoubleFunction) method:
Program 1:
// Java program to demonstrate Comparator// thenComparingDouble(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)    {        List<Student> list = getStudentList();          Comparator<Student> comparator            = Comparator                  .comparing(Student::getSchool)                  .thenComparingDouble(Student::getpercentageMarks);          Collections.sort(list, comparator);        System.out.println("After sort");        list.forEach(s -> System.out.println(s));    }      public static List<Student> getStudentList()    {          Student s1 = new Student("Ram", 85.5, "SJV");        Student s2 = new Student("Shyam", 83.25, "MSH");        Student s3 = new Student("Mohan", 86.55, "SJV");        Student s4 = new Student("Sohan", 81.00, "MSH");        Student s5 = new Student("Rabi", 55.6, "SJV");        List<Student> list = Arrays.asList(s1, s2, s3, s4, s5);          return list;    }}  class Student {      private String name;    private double percentageMarks;    private String school;      public Student(String name,                   double percentageMarks,                   String school)    {        this.name = name;        this.percentageMarks = percentageMarks;        this.school = school;    }      public String getName()    {        return name;    }      public void setName(String name)    {        this.name = name;    }      public double getpercentageMarks()    {        return percentageMarks;    }      public void setpercentageMarks(int percentageMarks)    {        this.percentageMarks = percentageMarks;    }      public String getSchool()    {        return school;    }      public void setSchool(String school)    {        this.school = school;    }      @Override    public String toString()    {        return "Student [name=" + name + ",             percentageMarks            = " + percentageMarks               + ", school=" + school + "]";    }} |
The output printed on console of IDE is shown below.
Output:
You can see in example first sorting is done on school wise and if the school is same then percentageMarks wise.
Program 2:
// Java program to demonstrate Comparator// thenComparingDouble(ToDoubleFunction) method  import java.util.Arrays;import java.util.Comparator;import java.util.List;  public class GFG {      public static void main(String... args)    {          List<Integer> list            = Arrays.asList(1, 2, 3, 4, 5, 6);          try {              // apply thenComparingDouble            Comparator.comparing(list::get)                .thenComparingDouble(null);        }        catch (Exception e) {              System.out.printf("Exception:" + e);        }    }} |
The output printed on console is shown below.
Output:
