Heap pollution
In the Java programming language, heap pollution is a situation that arises when a variable of a parameterized type refers to an object that is not of that parameterized type.[1] This situation is normally detected during compilation and indicated with an unchecked warning.[1] Later, during runtime heap pollution will often cause a ClassCastException.[2]
Heap pollution in Java can occur when type arguments and variables are not reified at run-time. As a result, different parameterized types are implemented by the same class or interface at run time. All invocations of a given generic type declaration share a single run-time implementation. This results in the possibility of heap pollution.[2]
Under certain conditions, a variable of a parameterized type may refer to an object that is not of that parameterized type. The variable will always refer to an object that is an instance of a class that implements the parameterized type.
Heap Pollution in a non-varargs context
public class HeapPollutionDemo { public static void main(String[] args) { Set s = new TreeSet<Integer>(); Set<String> ss = s; // unchecked warning s.add(new Integer(42)); // another unchecked warning Iterator<String> iter = ss.iterator(); while (iter.hasNext()) { String str = iter.next(); // ClassCastException thrown System.out.println(str); } } }
Further reading
- Gosling, James; Joy, Bill; Steele, Guy; Bracha, Gilad; Buckley, Alex (2014). "4.12.2". The Java Language Specification, Java SE 8 Edition. Addison-Wesley. pp. 81–82. ISBN 978-0-13-390069-9.
- Friesen, Jeff (2011). Beginning Java 7. Expert's voice in Java. Apress. p. 211. ISBN 978-1430239093.
- Reese, Richard; Reese, Jennifer (2012). Java 7 New Features Cookbook (PDF). Packt Publishing. pp. 38–40. ISBN 978-1-84968-562-7.
- Stenzel, Kurt; Grandy, Holger; Reif, Wolfgang (2008). "Verification of Java Programs with Generics". Algebraic Methodology and Software Technology. Lecture Notes in Computer Science. Vol. 5140. pp. 315–329. doi:10.1007/978-3-540-79980-1. ISBN 978-3-540-79979-5.(subscription required)
References
- ^ a b "The Java SE Tutorials". Oracle. Retrieved 16 July 2014.
- ^ a b Langer, Angelika. "Java Generics FAQs: Heap pollution". angelikalanger.com/. Retrieved 15 July 2014.
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