Unlike method overriding, in method overloading the choice of which method to invoke is determined at compile time. Even if the runtime type differs for each invocation, in overloading, the method invocations depend on the type of the object at compile time.
Noncompliant Code Example
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This noncompliant code example shows how the programmer can confuse overloading with overriding. At compile time, the type of the object array is {{List}}. The expected output is {{ArrayList}}, {{LinkedList}} and {{List is not recognized}} ({{java.util.Vector}} does not inherit from {{java.util.List}}). However, in all three instances {{List is not recognized}} gets displayed. This happens because in overloading, the method invocations are not affected by the runtime types but only the compile time type ({{List}}). It is dangerous to implement overloading to tally with overriding, more so, because the latter is characterized by inheritance unlike the former. \[[Bloch 08|AA. Java References#Bloch 08]\] |
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|---|---|---|
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public class Overloader {
private static String display(ArrayList<Integer> a) {
return "ArrayList";
}
private static String display(LinkedList<String> l) {
return "LinkedList";
}
private static String display(List<?> l) {
return "List is not recognized";
}
public static void main(String[] args) {
// Array of lists
List<?>[] invokeAll = new List<?>[] {new ArrayList<Integer>(),
new LinkedList<String>(), new Vector<Integer>()};
for(List<?> i : invokeAll) {
System.out.println(display(i));
}
}
} |
Compliant Solution
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This compliant solution uses a single {{display}} method and {{instanceof}} to distinguish between different types. As expected, the output is {{ArrayList, LinkedList, List is not recognized}}. As a general rule, do not introduce ambiguity while overloading so that the code is clean and easy to understand. \[[Bloch 08|AA. Java References#Bloch 08]\] |
| Code Block | ||
|---|---|---|
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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) {
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.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
MET33- J | low | unlikely | high | P1 | L3 |
Automated Detection
TODO
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
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\[[API 06|AA. Java References#API 06]\] [Interface Collection|http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collection.html] \[[Bloch 08|AA. Java References#Bloch 08]\] Item 41: Use overloading judiciously |
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