Programmer Misconceptions - Java Coding Guidelines - page 254

public static void main(String[] args) {
// Single ArrayList
System.out.println(display(new ArrayList<Integer>()));
// Array of lists
List<?>[] invokeAll = new List<?>[] {
new ArrayList<Integer>(),
new LinkedList<String>(),
new Vector<Integer>()};
for (List<?> list : invokeAll) {
System.out.println(display(list));
}
}
}
At compile time, the type of the object array is List . The expected output is Ar-
rayList , ArrayList , LinkedList , and List is not recognized (because
java.util.Vector is neither an ArrayList nor a LinkedList ). The actual output is Ar-
rayList followed by List is not recognized repeated three times. 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.
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 :
Click here to view code image
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>()));