DCL02-J. Do not overload variable argument methods

The varargs feature was introduced in the JDK v1.5.0. Its utility lies in allowing a method to accept a variable number of arguments.

According to [[Sun 06]] varargs documentation:

As an API designer, you should use them [varargs methods] sparingly, only when the benefit is truly compelling. Generally speaking, you should not overload a varargs method, or it will be difficult for programmers to figure out which overloading gets called.

Noncompliant Code Example

Overloading varargs methods can create confusion as shown in this noncompliant example. The programmer's intent was to invoke the variable argument (varargs) doSomething method, but instead its overloaded, more specific form took precedence.

class OverloadedVarargs {
  private static void doSomething(boolean... bool) {
    System.out.print("Number of arguments: " + bool.length + ", Contents: ");

    for (boolean b : bool)
      System.out.print("[" + b + "]");
  } 
  private static void doSomething(boolean bool1, boolean bool2) {
    System.out.println("Overloaded method invoked");  
  }
  public static void main(String[] args) {
    doSomething(true, false);
  }
}

Compliant Solution

Avoid overloading varargs methods. Use distinct method names so that the intended method gets invoked as prescribed by this compliant solution.

class NotOverloadedVarargs {
  private static void doSomething1(boolean... bool) {
    System.out.print("Number of arguments: " + bool.length + ", Contents: ");

    for (boolean b : bool)
      System.out.print("[" + b + "]");
  } 
  private static void doSomething2(boolean bool1, boolean bool2) {
    System.out.println("Overloaded method invoked");  
  }
  public static void main(String[] args) {
    doSomething1(true, false);
  }
}

Exceptions

*EX1:*Sometimes, it is desirable to violate the "do not overload varargs methods" advice for performance reasons (avoiding the cost of creation of an array instance and its initialization on every invocation of a varargs method). [[Bloch 08]]

public void foo() { }
public void foo(int a1) { }
public void foo(int a1, int a2, int... rest) { }

The idiom shown above avoids the pitfalls of incorrect method selection by using non-ambiguous method signatures and can consequently be discreetly used where required.

Risk Assessment

Unmindful use of the varargs feature may create ambiguity and diminish code readability.

Automated Detection

TODO

Related Vulnerabilities

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

References

[[Sun 06]] varargs
[[Bloch 08]] Item 42: "Use varargs judiciously"
[[Steinberg 05]] "Using the Varargs Language Feature"

DCL01-J. Use visually distinct identifiers      02. Declarations and Initialization (DCL)      03. Expressions (EXP)