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| Code Block | ||
|---|---|---|
| ||
public class Overloader {
private static String display(ArrayList<Integer> aarrayList) {
return "ArrayList";
}
private static String display(LinkedList<String> llinkedList) {
return "LinkedList";
}
private static String display(List<?> llist) {
return "List is not recognized";
}
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<?> ilist : invokeAll) {
System.out.println(display(ilist));
}
}
}
|
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].
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| Code Block | ||
|---|---|---|
| ||
class Overloader {
public class Overloader {
private static String display(List<?> llist) {
return (
llist instanceof ArrayList ? "Arraylist" :
(llist 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<?> ilist : invokeAll) {
System.out.println(display(ilist));
}
}
}
|
Appicability
Ambiguous uses of overloading can lead to unexpected results.
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