Java Collections.checkedSet() method

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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.checkedSet() method will returns a dynamically type safe view of the specified set.

Example

package com.w3schools;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
 
public class Test { 
    public static void main(String a[]){         
        Set set = new HashSet();
        set.add("vikas");
        set.add("mahesh");
        set.add("rahul");
        set.add("amit");
        Set checkedSet = Collections.checkedSet(set, String.class);
        System.out.println("Checked set content: "+checkedSet);
        set.add(10);      
        checkedSet.add(10); //throws ClassCastException
    }
}

Output

Checked set content: [mahesh, rahul, vikas, amit]
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.util.Collections$CheckedCollection.typeCheck(Collections.java:2202)
	at java.util.Collections$CheckedCollection.add(Collections.java:2243)
	at com.w3schools.Test.main(Test.java:16)

Java Collections class examples