The comparator() method of java.util.TreeMap class is used to return the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys.
--> java.util Package
--> TreeMap Class
--> comparator() Method
Syntax:
public Comparator comparator()
Return Type: This method returns the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys.
Note: descendingIterator() method is natural ordering by default.
Example 1: For Natural ordering
Java
import java.util.*;
public class GFG {
public static void main(String[] argv) throws Exception
{
try {
NavigableMap<Integer, String> treemap
= new TreeMap<Integer, String>();
treemap.put( 1 , "one" );
treemap.put( 2 , "two" );
treemap.put( 3 , "three" );
treemap.put( 4 , "four" );
treemap.put( 5 , "five" );
System.out.println( "TreeMap: " + treemap);
Comparator comp = treemap.comparator();
System.out.println( "Comparator value: " + comp);
}
catch (NullPointerException e) {
System.out.println( "Exception thrown : " + e);
}
}
}
|
Output: TreeMap: {1=one, 2=two, 3=three, 4=four, 5=five}
Comparator value: null
Example 2: For Reverse ordering
Java
import java.util.*;
public class GFG {
public static void main(String[] argv) throws Exception
{
try {
NavigableMap<Integer, String> treemap
= new TreeMap<Integer, String>(
Collections.reverseOrder());
treemap.put( 1 , "one" );
treemap.put( 2 , "two" );
treemap.put( 3 , "three" );
treemap.put( 4 , "four" );
treemap.put( 5 , "five" );
System.out.println( "TreeMap: " + treemap);
Comparator comp = treemap.comparator();
System.out.println( "Comparator value: " + comp);
}
catch (NullPointerException e) {
System.out.println( "Exception thrown : " + e);
}
}
}
|
Output: TreeMap: {5=five, 4=four, 3=three, 2=two, 1=one}
Comparator value: java.util.Collections$ReverseComparator@232204a1