DCL09-J. Enforce compile-time type checking of variable argument types

The Java compiler type-checks the arguments to a varargs method to ensure that they are of the same type or object reference. However, the compile-time checking is ineffective when two method signatures are used in particular - Object and the generic type T [[Bloch 2008]]. Another requirement for providing strong compile-time type checking of variable argument methods is to be as specific as possible when declaring the type of the method parameter.

Noncompliant Code Example

This noncompliant code example declares two methods, one with an Object parameter and another with a generic type T. Both these approaches are flawed as they break strong compile-time type checking.

ReturnType1 suspect1(Object... args) { }
<T> ReturnType2 suspect2(T... args) { }

Compliant Solution

Do not use generic types like Object in varargs and be as specific as possible when declaring parameter types.

ReturnType1 specific1(primitiveType1... args) { }
ReturnType2 specific2(primitiveType2... args) { }

Retrofitting old methods containing final array parameters with generically typed varargs is not always a good idea. This is because if some method did not accept an argument of a particular type, it may be possible to override the compile-time checking so that with the use of generic varargs, it now compiles cleanly [[Bloch 2008]].

Also, note that autoboxing does not allow strong compile time type checking of primitive types and their corresponding wrapper classes.

Risk Assessment

Unmindful use of the varargs feature breaks strong compile-time type checking, creates ambiguity and diminishes code readability.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Bibliography

[[Sun 2006]] varargs
[[Bloch 2008]] Item 42: "Use varargs judiciously"
[[Steinberg 2005]] "Using the Varargs Language Feature"

DCL08-J. Do not overload variable argument methods      03. Declarations and Initialization (DCL)      DCL10-J. Ensure proper initialization by declaring class and instance variables final