36 lines
1.1 KiB
Java
36 lines
1.1 KiB
Java
// generics/CheckedList.java
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// (c)2021 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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// Using Collection.checkedList()
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import reflection.pets.*;
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import java.util.*;
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public class CheckedList {
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@SuppressWarnings("unchecked")
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static void oldStyleMethod(List probablyDogs) {
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probablyDogs.add(new Cat());
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}
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public static void main(String[] args) {
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List<Dog> dogs1 = new ArrayList<>();
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oldStyleMethod(dogs1); // Quietly accepts a Cat
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List<Dog> dogs2 = Collections.checkedList(
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new ArrayList<>(), Dog.class);
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try {
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oldStyleMethod(dogs2); // Throws an exception
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} catch(Exception e) {
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System.out.println("Expected: " + e);
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}
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// Derived types work fine:
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List<Pet> pets = Collections.checkedList(
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new ArrayList<>(), Pet.class);
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pets.add(new Dog());
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pets.add(new Cat());
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}
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}
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/* Output:
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Expected: java.lang.ClassCastException: Attempt to
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insert class reflection.pets.Cat element into collection
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with element type class reflection.pets.Dog
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*/
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