330 Java Tips.pdf - FTP Server

General Java Questions I
System.err no. If you want to put both the "normal" output and the "error" output to a
file you must use the special redirect 2>.
This allow you to send normal messages into a file or in the /null black hole, but still
receive the error messages on the console.
What is the essential difference between an abstract class and an interface?
What dictates the choice of one over the other?
Answer: You can only extend one class (abstract or not) whereas you can always
implement one or more interfaces. Interfaces are Java's way to support multiple
inheritance.
Does anyone know how could I get the size of an Enumeration object? The API
for Enumeration only contains getNext() and next().
Answer 1: You can't. Theoretically, some classes that implement Enumeration may
also provide some way to get a size, but you'd have to know about the more specific
run-time type and cast to it... and none of the standard java.util Collections classes
nor Vector or such provide these methods in their Enumeration implementations.
Answer2:
you can make your own class like this:
import java.util.*;
public class MyEnumeration{
int size;
int index = 0;
Enumeration e;
}
public MyEnumeration(Vector v){
size = v.size();
e = v.elements();
index = 0;
}
public boolean hasMoreElements(){
return e.hasMoreElements();
}
public Object nextElement(){
index++;
return e.nextElement();
}
public int size(){
return size;
}
public int getIndex(){
return index;
}
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