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Do not introduce ambiguity while overloading (see [MET50-J. Avoid ambiguous uses of overloading]) and use overloaded methods sparingly \[[Tutorials 2010|AA. Bibliography#Tutorials 10]\] as they can make code much less readable. |
Noncompliant Code Example
This noncompliant code example attempts to use the overloaded display() method to perform different actions depending on whether the method is passed an ArrayList<Integer> or a LinkedList<String>.
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At compile time, the type of the object array is {{List}}. The expected output is {{ArrayList}}, {{ArrayList}}, {{LinkedList}} and {{List is not recognized}} ( because {{java.util.Vector}} does not inherit from {{java.util.List}}). The actual output is {{ArrayList}} followed by three instances of {{List is not recognized}}. The cause of this unexpected behavior is that overloaded method invocations are affected _only_ by the compile time type of their arguments: {{ArrayList}} for the first invocation and {{List}} for the others. Do not use overloading where overriding would be natural \[[Bloch 2008|AA. Bibliography#Bloch 08]\]. |
Compliant Solution
This compliant solution uses a single display method and instanceof to distinguish between different types. As expected, the output is ArrayList, ArrayList, LinkedList, List is not recognized.
| Code Block | ||
|---|---|---|
| ||
class Overloader {
public class Overloader {
private static String display(List<?> l) {
return (
l instanceof ArrayList ? "Arraylist" :
(l instanceof LinkedList ? "LinkedList" :
"List is not recognized")
);
}
public static void main(String[] args) {
// Single ArrayList
System.out.println(display(new ArrayList<Integer>()));
List<?>[] invokeAll = new List<?>[] {new ArrayList<Integer>(),
new LinkedList<String>(), new Vector<Integer>()};
for (List<?> i : invokeAll) {
System.out.println(display(i));
}
}
}
|
Risk Assessment
Ambiguous uses of overloading can lead to unexpected results.
Guideline | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
MET05-J | low | unlikely | high | P1 | L3 |
Automated Detection
Sound automated detection of violations is infeasible, because it would require determination of programmer intent. Heuristic techniques may be useful.
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this guideline on the CERT website.
Bibliography
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\[[API 2006|AA. Bibliography#API 06]\] [Interface Collection|http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collection.html] \[[Bloch 2008|AA. Bibliography#Bloch 08]\] Item 41: Use overloading judiciously \[[Tutorials 2010|AA. Bibliography#Tutorials 10]\] [Defining Methods|http://download.oracle.com/javase/tutorial/java/javaOO/methods.html] |
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