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:Â
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: Â
- 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 ClassCastExceptionÂ
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:Â
Example 1:
Java
// Java program to Demonstrate checkedMap() method// of Collections classÂ
// Importing required classesimport java.util.*;Â
// Main classpublic class GFG {Â
    // Main driver method    public static void main(String[] argv) throws Exception    {Â
        // Try block to check for exceptions        try {Â
            // Creating an empty HashMap by declaring            // HashMap key-value pairs            // of string and string type            HashMap<String, String> hmap                = new HashMap<String, String>();Â
            // Adding custom key-value pairs to above            // HashMap            hmap.put("Ram", "Shyam");            hmap.put("Karan", "Arjun");            hmap.put("Karn", "Veer");            hmap.put("duryodhan", "dhrupat");Â
            // Printing all the key-value pairs of above            // HashMap            System.out.println("Map: \n" + hmap);Â
            // 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);Â
            // Now printing the typesafe view of specified            // list            System.out.println("Typesafe view of Map: "                               + tsmap);        }Â
        // Catch block to handle the exceptions        catch (IllegalArgumentException e) {Â
            // Display message when exception occurs            System.out.println("Exception thrown : \n" + e);        }    }} |
Output:Â
Map:
{Karn=Veer, Karan=Arjun, duryodhan=dhrupat, Ram=Shyam}
Typesafe view of Map:
{Karn=Veer, Karan=Arjun, duryodhan=dhrupat, Ram=Shyam}
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Example 2:
Java
// Java program to demonstrate checkedMap() method// of Collections classÂ
// Importing all required classesimport java.util.*;Â
// Main classpublic class GFG {Â
    // Main driver method    public static void main(String[] argv) throws Exception    {Â
        // Try block to check for exceptions        try {Â
            // Creating an empty HashMap by            // declaring object of string and integer type            HashMap<String, Integer> hmap                = new HashMap<String, Integer>();Â
            // Adding key-value pairs to above HashMap            // object            hmap.put("Player-1", 20);            hmap.put("Player-2", 30);            hmap.put("Player-3", 40);Â
            // Printing the elements inside above HashMap            // object            System.out.println("Map: \n" + hmap);Â
            // Now creating typesafe view of the specified            // map using checkedMap() method            Map<String, Integer> tsmap                = Collections.checkedMap(hmap, String.class,                                         Integer.class);Â
            // Again printing the typesafe view of specified            // list            System.out.println("Typesafe view of Map: \n"                               + tsmap);        }Â
        // Catch block to handle exceptions        catch (IllegalArgumentException e) {Â
            // Display message when exception occurs            System.out.println("Exception thrown : " + e);        }    }} |
Output:Â
Map:
{Player-1=20, Player-3=40, Player-2=30}
Typesafe view of Map:
{Player-1=20, Player-3=40, Player-2=30}
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