36 lines
1.1 KiB
Java
36 lines
1.1 KiB
Java
// generics/CheckedList.java
|
|
// (c)2017 MindView LLC: see Copyright.txt
|
|
// We make no guarantees that this code is fit for any purpose.
|
|
// Visit http://OnJava8.com for more book information.
|
|
// Using Collection.checkedList()
|
|
import typeinfo.pets.*;
|
|
import java.util.*;
|
|
|
|
public class CheckedList {
|
|
@SuppressWarnings("unchecked")
|
|
static void oldStyleMethod(List probablyDogs) {
|
|
probablyDogs.add(new Cat());
|
|
}
|
|
public static void main(String[] args) {
|
|
List<Dog> dogs1 = new ArrayList<>();
|
|
oldStyleMethod(dogs1); // Quietly accepts a Cat
|
|
List<Dog> dogs2 = Collections.checkedList(
|
|
new ArrayList<>(), Dog.class);
|
|
try {
|
|
oldStyleMethod(dogs2); // Throws an exception
|
|
} catch(Exception e) {
|
|
System.out.println("Expected: " + e);
|
|
}
|
|
// Derived types work fine:
|
|
List<Pet> pets = Collections.checkedList(
|
|
new ArrayList<>(), Pet.class);
|
|
pets.add(new Dog());
|
|
pets.add(new Cat());
|
|
}
|
|
}
|
|
/* Output:
|
|
Expected: java.lang.ClassCastException: Attempt to
|
|
insert class typeinfo.pets.Cat element into collection
|
|
with element type class typeinfo.pets.Dog
|
|
*/
|