Guava - Ordering Class

Ordering can be seen as an enriched comparator with enhanced chaining functionality, multiple utility methods, multi-type sorting capability, etc.

Class Declaration

Following is the declaration for com.google.common.collect.Ordering<T> class:

@GwtCompatible
public abstract class Ordering<T>
   extends Object
      implements Comparator<T>

Class Methods

Sr.No	Method & Description
1	static Ordering<Object> allEqual() Returns an ordering which treats all values as equal, indicating "no ordering." Passing this ordering to any stable sort algorithm results in no change to the order of elements.
2	static Ordering<Object> arbitrary() Returns an arbitrary ordering over all objects, for which compare(a, b) == 0 implies a == b (identity equality).
3	int binarySearch(List<? extends T> sortedList, T key) Searches sortedList for key using the binary search algorithm.
4	abstract int compare(T left, T right) Compares its two arguments for order.
5	<U extends T> Ordering<U> compound(Comparator<? super U> secondaryComparator) Returns an ordering which first uses the ordering this, but which in the event of a "tie", then delegates to secondaryComparator.
6	static <T> Ordering<T> compound(Iterable<? extends Comparator<? super T>> comparators) Returns an ordering which tries each given comparator in order until a non-zero result is found, returning that result, and returning zero only if all comparators return zero.
7	static <T> Ordering<T> explicit(List<T> valuesInOrder) Returns an ordering that compares objects according to the order in which they appear in the given list.
8	static <T> Ordering<T> explicit(T leastValue, T... remainingValuesInOrder) Returns an ordering that compares objects according to the order in which they are given to this method.
9	static <T> Ordering<T> from(Comparator<T> comparator) Returns an ordering based on an existing comparator instance.
10	<E extends T> List<E> greatestOf(Iterable<E> iterable, int k) Returns the k greatest elements of the given iterable according to this ordering, in order from greatest to least.
11	<E extends T> List<E> greatestOf(Iterator<E> iterator, int k) Returns the k greatest elements from the given iterator according to this ordering, in order from greatest to least.
12	<E extends T> ImmutableList<E> immutableSortedCopy(Iterable<E> elements) Returns an immutable list containing elements sorted by this ordering.
13	boolean isOrdered(Iterable<? extends T> iterable) Returns true if each element in iterable after the first is greater than or equal to the element that preceded it, according to this ordering.
14	boolean isStrictlyOrdered(Iterable<? extends T> iterable) Returns true if each element in iterable after the first is strictly greater than the element that preceded it, according to this ordering
15	<E extends T> List<E> leastOf(Iterable<E> iterable, int k) Returns the k least elements of the given iterable according to this ordering, in order from least to greatest.
16	<E extends T> List<E> leastOf(Iterator<E> elements, int k) Returns the k least elements from the given iterator according to this ordering, in order from least to greatest.
17	<S extends T> Ordering<Iterable<S>> lexicographical() Returns a new ordering which sorts iterables by comparing corresponding elements pairwise until a nonzero result is found; imposes "dictionary order".
18	<E extends T> E max(E a, E b) Returns the greater of the two values according to this ordering.
19	<E extends T> E max(E a, E b, E c, E... rest) Returns the greatest of the specified values according to this ordering.
20	<E extends T> E max(Iterable<E> iterable) Returns the greatest of the specified values according to this ordering.
21	<E extends T> E max(Iterator<E> iterator) Returns the greatest of the specified values according to this ordering.
22	<E extends T> E min(E a, E b) Returns the lesser of the two values according to this ordering.
23	<E extends T> E min(E a, E b, E c, E... rest) Returns the least of the specified values according to this ordering.
24	<E extends T> E min(Iterable<E> iterable) Returns the least of the specified values according to this ordering.
25	<E extends T> E min(Iterator<E> iterator) Returns the least of the specified values according to this ordering.
26	static <C extends Comparable> Ordering<C> natural() Returns a serializable ordering that uses the natural order of the values.
27	<S extends T> Ordering<S> nullsFirst() Returns an ordering that treats null as less than all other values and uses this to compare non-null values.
28	<S extends T> Ordering<S> nullsLast() Returns an ordering that treats null as greater than all other values and uses this ordering to compare non-null values.
29	<F> Ordering<F> onResultOf(Function<F,? extends T> function) Returns a new ordering on F which orders elements by first applying a function to them, then comparing those results using this.
30	<S extends T> Ordering<S> reverse() Returns the reverse of this ordering; the Ordering equivalent to Collections.reverseOrder(Comparator).
31	<E extends T> List<E> sortedCopy(Iterable<E> elements) Returns a mutable list containing elements sorted by this ordering; use this only when the resulting list may need further modification, or may contain null.
32	static Ordering<Object> usingToString() Returns an ordering that compares objects by the natural ordering of their string representations as returned by toString().

Methods Inherited

This class inherits methods from the following class:

• java.lang.Object

Example of Ordering class

Create the following java program using any editor of your choice in say C:/> Guava.
GuavaTester.java

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import com.google.common.collect.Ordering;

public class GuavaTester {
   public static void main(String args[]) {
      List<Integer> numbers = new ArrayList<Integer>();
      
      numbers.add(new Integer(5));
      numbers.add(new Integer(2));
      numbers.add(new Integer(15));
      numbers.add(new Integer(51));
      numbers.add(new Integer(53));
      numbers.add(new Integer(35));
      numbers.add(new Integer(45));
      numbers.add(new Integer(32));
      numbers.add(new Integer(43));
      numbers.add(new Integer(16));

      Ordering ordering = Ordering.natural();
      System.out.println("Input List: ");
      System.out.println(numbers);  
         
      Collections.sort(numbers,ordering );
      System.out.println("Sorted List: ");
      System.out.println(numbers);
         
      System.out.println("======================");
      System.out.println("List is sorted: " + ordering.isOrdered(numbers));
      System.out.println("Minimum: " + ordering.min(numbers));
      System.out.println("Maximum: " + ordering.max(numbers));
         
      Collections.sort(numbers,ordering.reverse());
      System.out.println("Reverse: " + numbers);

      numbers.add(null);
      System.out.println("Null added to Sorted List: ");
      System.out.println(numbers);  

      Collections.sort(numbers,ordering.nullsFirst());
      System.out.println("Null first Sorted List: ");
      System.out.println(numbers);
      System.out.println("======================");

      List<String> names = new ArrayList<String>();
      
      names.add("Ram");
      names.add("Shyam");
      names.add("Mohan");
      names.add("Sohan");
      names.add("Ramesh");
      names.add("Suresh");
      names.add("Naresh");
      names.add("Mahesh");
      names.add(null);
      names.add("Vikas");
      names.add("Deepak");

      System.out.println("Another List: ");
      System.out.println(names);

      Collections.sort(names,ordering.nullsFirst().reverse());
      System.out.println("Null first then reverse sorted list: ");
      System.out.println(names);
   }
}

Verify the Result

Compile the class using javac compiler as follows:

C:\Guava>javac GuavaTester.java

Now run the GuavaTester to see the result.

C:\Guava>java GuavaTester

See the result.

Input List: 
[5, 2, 15, 51, 53, 35, 45, 32, 43, 16]
Sorted List: 
[2, 5, 15, 16, 32, 35, 43, 45, 51, 53]
======================
List is sorted: true
Minimum: 2
Maximum: 53
Reverse: [53, 51, 45, 43, 35, 32, 16, 15, 5, 2]
Null added to Sorted List: 
[53, 51, 45, 43, 35, 32, 16, 15, 5, 2, null]
Null first Sorted List: 
[null, 2, 5, 15, 16, 32, 35, 43, 45, 51, 53]
======================
Another List: 
[Ram, Shyam, Mohan, Sohan, Ramesh, Suresh, Naresh, Mahesh, null, Vikas, Deepak]
Null first then reverse sorted list: 
[Vikas, Suresh, Sohan, Shyam, Ramesh, Ram, Naresh, Mohan, Mahesh, Deepak, null]