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:
