Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
General <strong>Java</strong> Questions I<br />
System.err no. If you want to put both the "normal" output and the "error" output to a<br />
file you must use the special redirect 2>.<br />
This allow you to send normal messages into a file or in the /null black hole, but still<br />
receive the error messages on the console.<br />
What is the essential difference between an abstract class and an interface?<br />
What dictates the choice of one over the other?<br />
Answer: You can only extend one class (abstract or not) whereas you can always<br />
implement one or more interfaces. Interfaces are <strong>Java</strong>'s way to support multiple<br />
inheritance.<br />
Does anyone know how could I get the size of an Enumeration object? The API<br />
for Enumeration only contains getNext() and next().<br />
Answer 1: You can't. Theoretically, some classes that implement Enumeration may<br />
also provide some way to get a size, but you'd have to know about the more specific<br />
run-time type and cast to it... and none of the standard java.util Collections classes<br />
nor Vector or such provide these methods in their Enumeration implementations.<br />
Answer2:<br />
you can make your own class like this:<br />
import java.util.*;<br />
public class MyEnumeration{<br />
int size;<br />
int index = 0;<br />
Enumeration e;<br />
}<br />
public MyEnumeration(Vector v){<br />
size = v.size();<br />
e = v.elements();<br />
index = 0;<br />
}<br />
public boolean hasMoreElements(){<br />
return e.hasMoreElements();<br />
}<br />
public Object nextElement(){<br />
index++;<br />
return e.nextElement();<br />
}<br />
public int size(){<br />
return size;<br />
}<br />
public int getIndex(){<br />
return index;<br />
}<br />
file:///F|/350_t/350_tips/general_java-I.htm (8 of 31) [2002-02-27 21:18:17]