Not using checkedCollection:
package com.logicbig.example.collections;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
public class CheckedCollectionExample {
public static void main(String... args) {
Collection<String> c = new ArrayList<>();
Collections.addAll(c, "apple", "banana");
System.out.println(c);
Collection c2 = c;
c2.add(1);
System.out.println(c2);
}
}
Output
[apple, banana]
[apple, banana, 1]
Using checkedCollection:
package com.logicbig.example.collections;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
public class CheckedCollectionExample2 {
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);
Collection c2 = c;
c2.add(1);//this throws exception
System.out.println(c2);
}
}
Output
Caused by: java.lang.ClassCastException: Attempt to insert class java.lang.Integer element into collection with element type class java.lang.String
at java.util.Collections$CheckedCollection.typeCheck(Collections.java:3037)
at java.util.Collections$CheckedCollection.add(Collections.java:3080)
at com.logicbig.example.collections.CheckedCollectionExample2.main(CheckedCollectionExample2.java:22)
... 6 more