Java Collections checkedCollection() Method

The checkedCollection() is a method of Java Collections class which returns a dynamically typesafe view of the specified collection. If an element inserted of the wrong type, it will result in an immediate ClassCastException.

Syntax

Following is the declaration of checkedCollection() method:

public static <E> Collection<E> checkedCollection(Collection<E> c, Class<E> type)

Parameter

Parameter	Description	Required/Optional
c	It is the collection for which a dynamically typesafe view is to be returned.	Required
type	It is the type of element that c is permitted to hold.	Required

Returns

The checkedCollection() method returns a dynamically typesafe view of the specified collection.

Exceptions

ClassCastException

Compatibility Version

Java 1.5 and above

Example 1

import java.util.*;
public class CollectionsCheckedCollectionExample1 {
	public static void main(String[] args) {
		//Create list       
	      ArrayList<String> arrlist = new ArrayList<String>();
	      arrlist.add("A");
	      arrlist.add("B");
	      arrlist.add("C");
	      arrlist.add("D");
	      //Create type safe view of the collection
	      Collection<String> tslist;
	      tslist = Collections.checkedCollection(arrlist,String.class);     
	      System.out.println("Type safe view is: "+tslist);
	      }
}

Test it Now

Output:

Type safe view is: [A, B, C, D]

Example 2

import java.util.*;
public class CollectionsCheckedCollectionExample2 {
	public static void main(String[] args) {
		//Create list       
	      ArrayList<Integer> arrlist = new ArrayList<Integer>();
	      arrlist.add(10);
	      arrlist.add(20);
	      arrlist.add(30);
	      arrlist.add(40);
	      //Create type safe view of the collection
	      Collection<Integer> tsafelist;
	      tsafelist = Collections.checkedCollection(arrlist,Integer.class);     
	      System.out.println("Type safe view is: "+tsafelist);
	      }
}

Test it Now

Output:

Type safe view is: [10, 20, 30, 40]

Example 3

import java.util.*;
public class CollectionsCheckedCollectionExample3 {
	public static void main(String[] args) {
            Collection<String> c = new ArrayList<>();
            c = Collections.checkedCollection(c, String.class);
            Collections.addAll(c, "apple", "banana");
            System.out.println(c);
            @SuppressWarnings("rawtypes")
		Collection c2 = c;
            c2.add(1);//this throws exception
            System.out.println(c2);
		}
}

Test it Now

Output:

[apple, banana]
Exception in thread "main" java.lang.ClassCastException: Attempt to insert class java.lang.Integer element into collection with element type class java.lang.String
	at java.base/java.util.Collections$CheckedCollection.typeCheck(Collections.java:3038)
	at java.base/java.util.Collections$CheckedCollection.add(Collections.java:3081)
	at myPackage.CollectionCheckedCollectionExample3.main(CollectionCheckedCollectionExample3.java:12)

Next TopicJava Collections Class

← prev next →