Guava – Ordering Class

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.NOMETHOD & 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]

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