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 classesimport java.util.*;// Main classpublic 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); } }} |
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 classesimport java.util.*;// Main classpublic 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); } }} |
Map:
{Player-1=20, Player-3=40, Player-2=30}
Typesafe view of Map:
{Player-1=20, Player-3=40, Player-2=30}
