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Java Collections - Collections.checkedSet() Examples

Java Collections Java Java API 

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Class:

java.util.Collections

java.lang.Objectjava.lang.Objectjava.util.Collectionsjava.util.CollectionsLogicBig

Method:

public static <E> Set<E> checkedSet(Set<E> s,
                                    Class<E> type)

Returns a dynamically typesafe view of the specified Set.


Examples


package com.logicbig.example.collections;

import java.util.HashSet;
import java.util.Set;

public class CheckedSetExample {

    public static void main(String... args) {
        Set<Integer> set = new HashSet<>();
        set.add(1);
        System.out.println(set);

        Set set2 = set;
        set2.add("two");
        System.out.println(set2);
    }
}

Output

[1]
[1, two]




Using checkedSet: 

package com.logicbig.example.collections;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

public class CheckedSetExample2 {

    public static void main(String... args) {
        Set<Integer> set = new HashSet<>();
        set = Collections.checkedSet(set, Integer.class);
        set.add(1);
        System.out.println(set);

        Set set2 = set;
        set2.add("two");
        System.out.println(set2);
    }
}

Output

Caused by: java.lang.ClassCastException: Attempt to insert class java.lang.String element into collection with element type class java.lang.Integer
	at java.util.Collections$CheckedCollection.typeCheck(Collections.java:3037)
	at java.util.Collections$CheckedCollection.add(Collections.java:3080)
	at com.logicbig.example.collections.CheckedSetExample2.main(CheckedSetExample2.java:22)
	... 6 more

See Also