Java Collections.checkedMap() method

by

The java.util.Collections class consists exclusively of static methods that operate on or return collections. It contains polymorphic algorithms that operate on collections, “wrappers”, which return a new collection backed by a specified collection, and a few other odds and ends.

Collections.checkedMap() method will returns a dynamically typesafe view of the specified map.
Syntax: public static Map checkedMap(Map m,Class keyType,Class valueType)

Example

package com.w3schools;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
 
public class Test { 
    public static void main(String a[]){         
    	Map map = new HashMap();
    	map.put("vikas",1);
    	map.put("mahesh",2);
    	map.put("rahul",3);
    	map.put("amit",4);
        Map chekedMap = Collections.checkedMap(map, String.class, Integer.class);
        System.out.println("Checked Map content: "+chekedMap);
        map.put(5,"ajay");        
        chekedMap.put(6,"anil"); //throws ClassCastException
    }
}

Output

Checked Map content: {mahesh=2, rahul=3, vikas=1, amit=4}
Exception in thread "main" java.lang.ClassCastException: Attempt to insert class java.lang.Integer key into collection with key type class java.lang.String
	at java.util.Collections$CheckedMap.typeCheck(Collections.java:2547)
	at java.util.Collections$CheckedMap.put(Collections.java:2579)
	at com.w3schools.Test.main(Test.java:18)

Java Collections class examples