Collections checkedCollection() method in Java with Examples

The checkedCollection() method of java.util.Collections class is used to return a dynamically typesafe view of the specified collection. The returned collection does not pass the hashCode and equals operations through to the backing collection, but relies on Object’s equals and hashCode methods. This is necessary to preserve the contracts of these operations in the case that the backing collection is a set or a list. The returned collection will be serializable if the specified collection is serializable.
Since null is considered to be a value of any reference type, the returned collection permits insertion of null elements whenever the backing collection does.

Syntax:

public static  Collection 
checkedCollection(Collection c, Class type)

Parameters: This method takes two parameters 

• The collection for which a dynamically typesafe view is to be returned
• The type of element that c is permitted to hold

Return Type: This method returns a dynamically typesafe view of the specified collection

Example 1:

Java

// Java program to demonstrate
// checkedCollection() method
// for String value

// Importing utility classes
import java.util.*;

// Main class
public class GFG {

    // Main driver method
    public static void main(String[] argv) throws Exception
    {

        // Try block to check for exceptions
        try {

            // Creating an empty ArrayList by
            // creating object of List of string type
            List<String> arlst = new ArrayList<String>();

            // Adding element to arrlist
            // using add() method

            // Custom input elements
            arlst.add("CSS");
            arlst.add("PHP");
            arlst.add("HTML");
            arlst.add("TajMahal");

            // Printing the ArrayList
            System.out.println("List: " + arlst);

            // Now create typesafe view of the collection by
            // creating object of Collection class of string
            // type
            Collection<String> tslst
                = Collections.checkedCollection(
                    arlst, String.class);

            // Printing the updated ArrayList
            // after applying checkedCollection() method
            System.out.println("Typesafe view of List: "
                               + tslst);
        }

        // Catch block to handle the exceptions
        catch (IllegalArgumentException e) {

            // Print message to be displayed on console
            // when exception occurs
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

List: [CSS, PHP, HTML, TajMahal]
Typesafe view of List: [CSS, PHP, HTML, TajMahal]

Example 2:

Java

// Java program to Illustrate checkedCollection() method
// of Collection class for an Integer value

// Importing classes
import java.util.*;

// Main class
public class GFG {

    // Main driver method
    public static void main(String[] argv) throws Exception
    {

        // Try block to check for exception
        try {

            // Creating an empty ArrayList of integer type
            // by declaring object of List
            List<Integer> arlst = new ArrayList<Integer>();

            // Adding element to ArrayList
            // using add() method
            arlst.add(20);
            arlst.add(30);
            arlst.add(40);
            arlst.add(50);

            // Printing the above ArrayList
            System.out.println("List: " + arlst);

            // now creating typesafe view of the collection
            // using checkedCollection() method
            Collection<Integer> tslst
                = Collections.checkedCollection(
                    arlst, Integer.class);

            // Printing the updated ArrayList
            // after above operation
            System.out.println("Typesafe view of List: "
                               + tslst);
        }

        // Catch block to handle exceptions
        catch (IllegalArgumentException e) {

            // Display message if exception occurs
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

List: [20, 30, 40, 50]
Typesafe view of List: [20, 30, 40, 50]