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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}} is 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. \[[Bloch 2008|AA. Java References#Bloch 08]\]

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));
    }
  }
}

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. \[[Bloch 2008|AA. Java References#Bloch 08]\]

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));
    }
  }
}

\[[API 2006|AA. Java References#API 06]\] [Interface Collection|http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collection.html]
\[[Bloch 2008|AA. Java References#Bloch 08]\] Item 41: Use overloading judiciously