Ordering Class | Guava | Java

A comparator, with additional methods to support common operations. This is an “enriched” version of Comparator. The common ways to get an instance of Ordering are :

• Subclass it and implement compare(T, T) instead of implementing Comparator directly.
• Pass a pre-existing Comparator instance to from(Comparator).
• Use the natural ordering, natural().

Declaration : The declaration for com.google.common.collect.Ordering<T> class is :

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

Below given are some methods provided by Guava’s Ordering Class :

Ordering() : This is a constructor of Ordering Class of Guava. It constructs a new instance of this class (only invokable by the subclass constructor, typically implicit). Some other methods provided by this Class are :

Exceptions :

• explicit(List valuesInOrder) : NullPointerException if any of the provided values is null, IllegalArgumentException if valuesInOrder contains any duplicate values.
• explicit(T leastValue, T… remainingValuesInOrder) : NullPointerException if any of the provided values is null, IllegalArgumentException if any duplicate values.
• min(Iterator iterator) : NoSuchElementException if iterator is empty, ClassCastException if the parameters are not mutually comparable under this ordering.
• min(Iterable iterable) : NoSuchElementException if iterable is empty, ClassCastException if the parameters are not mutually comparable under this ordering.
• min(E a, E b) : ClassCastException if the parameters are not mutually comparable under this ordering.
• min(E a, E b, E c, E… rest) : ClassCastException if the parameters are not mutually comparable under this ordering.
• max(Iterator iterator) : NoSuchElementException if iterator is empty, ClassCastException if the parameters are not mutually comparable under this ordering.
• max(Iterable iterable) : NoSuchElementException if iterable is empty, ClassCastException if the parameters are not mutually comparable under this ordering.
• max(E a, E b) : ClassCastException if the parameters are not mutually comparable under this ordering.
• max(E a, E b, E c, E… rest) : ClassCastException if the parameters are not mutually comparable under this ordering.
• leastOf(Iterable iterable, int k): IllegalArgumentException if k is negative.
• leastOf(Iterator elements, int k) : IllegalArgumentException if k is negative.
• greatestOf(Iterable iterable, int k): IllegalArgumentException if k is negative.
• greatestOf(Iterator elements, int k) : IllegalArgumentException if k is negative.
• immutableSortedCopy : NullPointerException if any of elements (or elements itself) is null.

Some other methods provided by this class are :

Example 1 :

// Java code to show implementation of
// Ordering class
import java.util.*;

import com.google.common.collect.Ordering;

class GFG {

    // Driver code
    public static void main(String args[])
    {

        // Creating a list of Integers
        List<Integer> myList = new ArrayList<Integer>();

        myList.add(new Integer(12));
        myList.add(new Integer(3));
        myList.add(new Integer(78));
        myList.add(new Integer(50));
        myList.add(new Integer(6));
        myList.add(new Integer(70));
        myList.add(new Integer(18));
        myList.add(new Integer(9));
        myList.add(new Integer(10));

        // Displaying natural order of numbers
        Ordering ordering = Ordering.natural();
        System.out.println("Input List : " + myList);

        // Displaying the sorted list
        Collections.sort(myList, ordering);
        System.out.println("Sorted List : " + myList);
    }
}

Output :

Input List : [12, 3, 78, 50, 6, 70, 18, 9, 10]
Sorted List : [3, 6, 9, 10, 12, 18, 50, 70, 78]

Below given are some other methods provided by Ordering Class of Guava :

Example 2 :

// Java code to show implementation of
// Ordering class
import java.util.*;

import com.google.common.collect.Ordering;

class GFG {

    // Driver code
    public static void main(String args[])
    {

        // Creating a list of Integers
        List<Integer> myList = new ArrayList<Integer>();

        myList.add(new Integer(12));
        myList.add(new Integer(3));
        myList.add(new Integer(78));
        myList.add(new Integer(50));
        myList.add(new Integer(6));
        myList.add(new Integer(70));
        myList.add(new Integer(18));
        myList.add(new Integer(9));
        myList.add(new Integer(10));

        // Displaying natural order of numbers
        Ordering ordering = Ordering.natural();
        System.out.println("Minimum element is : " + ordering.min(myList));
    }
}

Output :

Minimum element is : 3

Example 3 :

// Java code to show implementation of
// Ordering class
import java.util.*;

import com.google.common.collect.Ordering;

class GFG {

    // Driver code
    public static void main(String args[])
    {

        // Creating a list of Integers
        List<Integer> myList = new ArrayList<Integer>();

        myList.add(new Integer(12));
        myList.add(new Integer(3));
        myList.add(new Integer(78));
        myList.add(new Integer(50));
        myList.add(new Integer(6));
        myList.add(new Integer(70));
        myList.add(new Integer(18));
        myList.add(new Integer(9));
        myList.add(new Integer(10));

        // Displaying natural order of numbers
        Ordering ordering = Ordering.natural();
        System.out.println("Maximum element is : " + ordering.max(myList));
    }
}

Output :

Maximum element is : 78

Example 4 :

// Java code to show implementation of
// Ordering class
import java.util.*;

import com.google.common.collect.Ordering;

class GFG {

    // Driver code
    public static void main(String args[])
    {

        // Creating a list of Integers
        List<Integer> myList = new ArrayList<Integer>();

        myList.add(new Integer(12));
        myList.add(new Integer(3));
        myList.add(new Integer(78));
        myList.add(new Integer(50));
        myList.add(new Integer(6));
        myList.add(new Integer(70));
        myList.add(new Integer(18));
        myList.add(new Integer(9));
        myList.add(new Integer(10));

        // Displaying natural order of numbers
        Ordering ordering = Ordering.natural();

        // To get reverse of original list
        Collections.sort(myList, ordering.reverse());

        // Displaying the reversed elements
        System.out.println(myList);
    }
}

Output :

[78, 70, 50, 18, 12, 10, 9, 6, 3]

Reference : Google Guava