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 ClassCast Exception. ^[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

publicclassHeapPollutionDemo{publicstaticvoidmain(String[]args){Sets=newTreeSet<Integer>();Set<String>ss=s;// unchecked warnings.add(newInteger(42));// another unchecked warningIterator<String>iter=ss.iterator();while(iter.hasNext()){Stringstr=iter.next();// ClassCastException thrownSystem.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

1. "The Java SE Tutorials". Oracle. Retrieved 16 July 2014.
2. Langer, Angelika. "Java Generics FAQs: Heap pollution". angelikalanger.com/. Retrieved 15 July 2014.