Collections checkedMap() method in Java with Examples

The checkedMap() method of Collections class been present inside java.util package is used to return a dynamically typesafe view of the specified map. The returned map will be serializable if the specified map is serializable. Since null is considered to be a value of any reference type, the returned map permits the insertion of null keys or values whenever the backing map does.

Syntax:

public static  Map 
checkedMap(Map m, Class keyType, Class valueType)

Parameters: This method takes the following 3 arguments as a parameter as listed below as follows:  

• Map for which a dynamically typesafe view is to be returned
• Type of key that m is permitted to hold
• Type of value that m is permitted to hold

Return Value: This method returns a dynamically typesafe view of the specified map.

Exceptions: This method does throw ClassCastException

Tip: This method is compatible with java version 1.5 and onwards.

Now let us see a few examples in order to implement the above method and to get a better understanding of the method which is as follows: 

Example 1:

Java

// Java program to Demonstrate checkedMap() method
// of Collections class

// Importing required 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 HashMap by declaring
            // HashMap key-value pairs
            //  of string and string type
            HashMap<String, String> hmap
                = new HashMap<String, String>();

            // Adding custom key-value pairs to above
            // HashMap
            hmap.put("Ram", "Shyam");
            hmap.put("Karan", "Arjun");
            hmap.put("Karn", "Veer");
            hmap.put("duryodhan", "dhrupat");

            // Printing all the key-value pairs of above
            // HashMap
            System.out.println("Map: \n" + hmap);

            // Now creating typesafe view of the specified
            // map using checkedMap() method of Collections
            // class
            Map<String, String> tsmap
                = Collections.checkedMap(hmap, String.class,
                                         String.class);

            // Now printing the typesafe view of specified
            // list
            System.out.println("Typesafe view of Map: "
                               + tsmap);
        }

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

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

Output:

Map: 
{Karn=Veer, Karan=Arjun, duryodhan=dhrupat, Ram=Shyam}
Typesafe view of Map: 
{Karn=Veer, Karan=Arjun, duryodhan=dhrupat, Ram=Shyam}

Example 2:

Java

// Java program to demonstrate checkedMap() method
// of Collections class

// Importing all required 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 HashMap by
            // declaring object of string and integer type
            HashMap<String, Integer> hmap
                = new HashMap<String, Integer>();

            // Adding key-value pairs to above HashMap
            // object
            hmap.put("Player-1", 20);
            hmap.put("Player-2", 30);
            hmap.put("Player-3", 40);

            // Printing the elements inside above HashMap
            // object
            System.out.println("Map: \n" + hmap);

            // Now creating typesafe view of the specified
            // map using checkedMap() method
            Map<String, Integer> tsmap
                = Collections.checkedMap(hmap, String.class,
                                         Integer.class);

            // Again printing the typesafe view of specified
            // list
            System.out.println("Typesafe view of Map: \n"
                               + tsmap);
        }

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

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

Output:

Map: 
{Player-1=20, Player-3=40, Player-2=30}
Typesafe view of Map: 
{Player-1=20, Player-3=40, Player-2=30}