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Do not introduce ambiguity while overloading (see 71. MET50-JG. Avoid ambiguous or confusing uses of overloading), and use overloaded methods sparingly [Tutorials 2008], because 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].

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:

class Overloader {
public class Overloader {
  private static String display(List<?> list) {
    return (
      list instanceof ArrayList ? "Arraylist" : 
      (list 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<?> list : invokeAll) {
      System.out.println(display(list));
    }
  }
}

Applicability

Ambiguous uses of overloading can lead to unexpected results.

Bibliography

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