Java Collections checkedMap() Method

The checkedMap() is an inbuilt method of Java Collections class. This method is used to get a dynamically typesafe view of the specified Map. If any attempt of insert mapping whose key or value has the wrong type, it will result in an immediate ClassCastException.

Syntax

Following is the declaration of checkedMap() method:

public static <K,V> Map<K,V> checkedMap(Map<K,V> m, Class<K> keyType, Class<V> valueType)	

Parameter

Parameter	Description	Required/Optional
m	It is the map for which a dynamically typesafe view is to be returned.	Required
keyType	It is the type of key that map m is permitted to hold.	Required
valueType	It is the type of value that map m is permitted to hold.	Required

Returns

The checkedMap() method returns a dynamically typesafe view of the specified Map.

Exceptions

ClassCastException

Compatibility Version

Java 1.5 and above

Example 1

import java.util.*;
public class CollectionsCheckedMapExample1 {
	public static void main(String[] args) {
		//create map     
	      HashMap<String, Integer> hmap = new HashMap<String, Integer>();
	      //Insert values in the Map
	      hmap.put("A", 11);
	      hmap.put("B", 12);
	      hmap.put("C", 13);
	      hmap.put("V", 14);
	      //Create type safe view of the Map         
	      System.out.println("Type safe view of the Map is: "+Collections.checkedMap(hmap,String.class,Integer.class));
	      }
}

Test it Now

Output:

Type safe view of the Map is: {A=11, B=12, C=13, V=14}

Example 2

import java.util.*;
public class CollectionsCheckedMapExample2 {
	public static void main(String[] args) {
		Map<Integer, String> map = new HashMap<Integer, String>();
            map.put(1, "One");
            map.put(2, "Two");
            map.put(3, "Three");
            System.out.println("Map  Element: "+map);
            Map map2 = map;
            map2.put("Four", 4);
            System.out.println(map2);
	      }
}

Test it Now

Output:

Map  Element: {1=One, 2=Two, 3=Three}
{1=One, 2=Two, 3=Three, Four=4}

Example 3

package myPackage;
import java.util.*;
public class CollectionsCheckedMapExample3 {
	public static void main(String[] args) {
		Map map = new HashMap();
    	      map.put("Raj",1);
    	      map.put("JavaTpoint",2);
    	      map.put("Rahul",3);
    	      map.put("Amit",4);
         Map chekedMap = Collections.checkedMap(map, String.class, Integer.class);
            System.out.println("Map content: "+chekedMap);
            map.put(5,"Karan");        
            chekedMap.put(6,"Akhil"); //throws ClassCastException
	      }
}

Test it Now

Output:

Map content: {Rahul=3, Amit=4, Raj=1, JavaTpoint=2}
Exception in thread "main" java.lang.ClassCastException: Attempt to insert class java.lang.Integer key into map with key type class java.lang.String
	at java.base/java.util.Collections$CheckedMap.typeCheck(Collections.java:3575)
	at java.base/java.util.Collections$CheckedMap.put(Collections.java:3621)
	at myPackage.CollectionCheckedMapExample3.main(CollectionCheckedMapExample3.java:13)

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