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: