Java - The Collection Algorithms

The collections framework defines several algorithms that can be applied to collections and maps.

These algorithms are defined as static methods within the Collections class. Several of the methods can throw a ClassCastException, which occurs when an attempt is made to compare incompatible types, or an UnsupportedOperationException, which occurs when an attempt is made to modify an unmodifiable collection.

The methods defined in collection framework's algorithm are summarized in the following table −

Example 1

Following is an example, which demonstrates various algorithms using LinkedList to add elements and sort its elements in reverse order. Using iterator, list is iterated then shuffled and lastly minimum and maximum values are retrieved and printed.

import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
public class AlgorithmsDemo {

   public static void main(String args[]) {
      
      // Create and initialize linked list
      List<Integer< ll = new LinkedList<<();
      ll.add(Integer.valueOf(-8));
      ll.add(Integer.valueOf(20));
      ll.add(Integer.valueOf(-20));
      ll.add(Integer.valueOf(8));
      
      // Create a reverse order comparator
      Comparator<Integer< r = Collections.reverseOrder();
      
      // Sort list by using the comparator
      Collections.sort(ll, r);
      
      // Get iterator
      Iterator<Integer< li = ll.iterator();
      System.out.print("List sorted in reverse: ");
      
      while(li.hasNext()) {
         System.out.print(li.next() + " ");
      }
      System.out.println();
   }
}

Output

List sorted in reverse: 20 8 -8 -20

Example 2

Following is an example, which demonstrates various algorithms using LinkedList to add elements and sort its elements in natural order. Using iterator, list is iterated then shuffled and lastly minimum and maximum values are retrieved and printed.

import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
public class AlgorithmsDemo {

   public static void main(String args[]) {
      
      // Create and initialize linked list
      List<Integer> ll = new LinkedList<>();
      ll.add(Integer.valueOf(-8));
      ll.add(Integer.valueOf(20));
      ll.add(Integer.valueOf(-20));
      ll.add(Integer.valueOf(8));
      
      
      // Sort list by using the default comparator
      Collections.sort(ll);
      
      // Get iterator
      Iterator<Integer> li = ll.iterator();
      System.out.print("List sorted: ");
      
      while(li.hasNext()) {
         System.out.print(li.next() + " ");
      }
      System.out.println();
      Collections.shuffle(ll);
      
      // display randomized list
      li = ll.iterator();
      System.out.print("List shuffled: ");
      
      while(li.hasNext()) {
         System.out.print(li.next() + " ");
      }

      System.out.println();
      System.out.println("Minimum: " + Collections.min(ll));
      System.out.println("Maximum: " + Collections.max(ll));
   }
}

Output

List sorted: -20 -8 8 20 
List shuffled: -20 -8 20 8 
Minimum: -20
Maximum: 20

Example 3

Following is an example, which demonstrates various algorithms using LinkedList to add String elements and sort its elements in natural order. List is printed then shuffled and lastly minimum and maximum values are retrieved and printed.

import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

public class AlgorithmsDemo {

   public static void main(String args[]) {

      // Create and initialize linked list
      List<String> list = new LinkedList<>();
      list.add("Ram");
      list.add("Mohan");
      list.add("Julie");
      list.add("Raheem");

      // Sort list by using the default comparator
      Collections.sort(list);

      // print the sorted list
      System.out.println("Sorted List: " + list);

      // shuffle the list
      Collections.shuffle(list);

      // print the shuffled list
      System.out.println("Shuffled List: " + list);

      System.out.println("Minimum: " + Collections.min(list));
      System.out.println("Maximum: " + Collections.max(list));
   }
}

Output

Sorted List: [Julie, Mohan, Raheem, Ram]
Shuffled List: [Mohan, Raheem, Julie, Ram]
Minimum: Julie
Maximum: Ram