Question about Math Class

I have a couple of Java questions I was wondering if anyone could answer:
1). In this one statement, which takes the greatest common denominator and places it in the variable commom:
int common = gcd (Math.abs(numerator), denominator);
A).What is gcd? I looked it up and it's not a reserved word in the math class. In the class that this statement comes from there is no variable, object, or method named gcd. There is also no gcd variable, object, or invoked method in the client code that uses the class that this statement comes from.
B ). I know that abs is a method of the math class for the absolute value of a number(in this case the number inside the variable numerator.). And I know that when the abs method is invoked it sends the variable 'numerator' as the parameter for the data to take the absolute value of. What I don't understand is the syntax of this statement in regards to how you can take the absolute value of the variable 'denominator' haveing a variable 'numerator' inclosed in the parenthesis and simpley adding a comma to include the variable 'denominator' in the argument to be sent in the invocation of the abs method. It seems like this would be the correct syntax:
int common = (Math.abs(numerator))/(Math.abs(denominator));
Can anyone explain the 'int common = gcd (Math.abs(numerator), denominator);'
statement?
Thanks,
-dman

> A).What is gcd?
As already been said: it's the Greatest Common Divider.
Example: fraction 9/24, then gcd(9, 24) == 3.
>It seems like this would be the correct syntax:
int common = (Math.abs(numerator))/(Math.abs(denominator));
Probably the gcd(...) method is used to normalize a fraction whose denominator is always positive. If the fraction is smaller then zero, the numerator is negative. And to caculate the Greatest Common Divider of two numbers, the gcd(...) method needs two positive arguments.
Google for "Euclid GCD algorithm".

Similar Messages

A question about Object Class

I got a question about Object class in AS3 recently.
I typed some testing codes as following:
var cls:Class = Object;
var cst:* = Object.prototype.constructor;
trace( cls === cst); // true
so cls & cst are the same thing ( the Object ).
var obj:Object = new Object();
var cst2:* = obj.constructor.constructor;
var cst3:* = obj.constructor.constructor.c.constructor;
var cst5:* = Object.prototype.constructoronstructor;
var cst4:* = Object.prototype.constructor.constructor.constructor;
var cst6:* = cls.constructor;
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but
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I used "describeType" and found that "cst2" is actually "Class" class.
So,
trace(cst2 === Class); // true
That's what I want to know, Thank you.

Question about inner class - help please

hi all
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for this case, i do need to create a new instance of
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Question about abstract classes and instances

I have just read about abstract classes and have learned that they cannot be instantiated.
I am doing some exercises and have done a class named "Person" and an abstract class named "Animal".
I want to create a method in "Person" that makes it possible to set more animals to Person objects.
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Roxxor wrote:
Ok, but why is it necessary with constructors in abstract classes if we don�t use them (because what I have understand, constructors are used to create objects)?Constructors don't create objects. The new operator creates objects. An object's c'tor is invoked after the object has already been created. The c'tors job is to initialize the newly-created object to a valid state. Whenever a child object is created, the parent's c'tor is run before the child's c'tor, so that by the time we're inside the child's c'tor, setting up the child's state, we know that the parent (or rather the "parent part" of the object we're initializing) is in a valid state.
Constructor rules:
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1.1) If you do not define an explicit constructor for your class, the compiler provides a implicit constructor that takes no args and simply calls super().
1.2) If you do define one or more explicit constructors, regardless of whether they take args, then the compiler no longer provides the implicit no-arg ctor. In this case, you must explicitly define a public MyClass() {...} if you want one.
1.3) Constructors are not inherited.
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Question about multiple class files

I just started learning JAVA a couple of days ago and the first program I wrote had two classes in one file. here is the program :
class fib_num {
public int value;
public boolean is_even;
class Fibonacci {
/** Print the Fibonacci sequence for values < MAX and mark even numbers with an asterick */
private static final int MAX = 50;
private static final String Title = "The Fibonacci sequence for values less than " + MAX + ":";
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//references to objects of the fib_num class
public static void main(String[] args) {
System.out.println(Title);
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fib = new fib_num();
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for (int i = 2; i < fib.length; i += 1) {
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hi = lo + hi;
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}else {
fib.is_even = false;
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if (array == null || array.length == 0)
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String mark;
for (int i = 0; array.value < MAX; i += 1) {
if (array.is_even) {
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}else {
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I ran the program and everything went fine. But today I started to write another program with two classes. However the file will not compile and I get an error about interfacing or something. here is the program:
Note: it's not nearly complete.
class enumerate {
//print out all permutations of a list of integers
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public static int[] initialize(int[] nums) {
for (int i = 0; i < nums.length; i++) {
nums = i + 1;
return nums;
public static void print(int[] nums) {
for (int i = 0; i < nums.length; i++) {
System.out.print(nums);
System.out.println("");
public static void swap (int[] nums, int i, int j) {
int temp = nums;
nums = nums[j];
nums[j] = temp;
public static void main (String[] args) {
int[] list = new int[MAX];
list = initialize(list);
PermutationGenerator x = new PermutationGenerator(5);
// Systematically generate permutations.
import java.math.BigInteger;
public class PermutationGenerator {
private int[] a;
private BigInteger numLeft;
private BigInteger total;
// Constructor. WARNING: Don't make n too large.
// Recall that the number of permutations is n!
// which can be very large, even when n is as small as 20 --
// 20! = 2,432,902,008,176,640,000 and
// 21! is too big to fit into a Java long, which is
// why we use BigInteger instead.
public PermutationGenerator (int n) {
if (n < 1) {
throw new IllegalArgumentException ("Min 1");
a = new int[n];
total = getFactorial (n);
reset ();
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public void reset () {
for (int i = 0; i < a.length; i++) {
a = i;
numLeft = new BigInteger (total.toString ());
// Return number of permutations not yet generated
public BigInteger getNumLeft () {
return numLeft;
// Return total number of permutations
public BigInteger getTotal () {
return total;
// Are there more permutations?
public boolean hasMore () {
return numLeft.compareTo (BigInteger.ZERO) == 1;
// Compute factorial
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BigInteger fact = BigInteger.ONE;
for (int i = n; i > 1; i--) {
fact = fact.multiply (new BigInteger (Integer.toString (i)));
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public int[] getNext () {
if (numLeft.equals (total)) {
numLeft = numLeft.subtract (BigInteger.ONE);
return a;
int temp;
// Find largest index j with a[j] < a[j+1]
int j = a.length - 2;
while (a[j] > a[j+1]) {
j--;
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// greater than a[j] to the right of a[j]
int k = a.length - 1;
while (a[j] > a[k]) {
k--;
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temp = a[k];
a[k] = a[j];
a[j] = temp;
// Put tail end of permutation after jth position in increasing order
int r = a.length - 1;
int s = j + 1;
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temp = a[s];
a[s] = a[r];
a[r] = temp;
r--;
s++;
numLeft = numLeft.subtract (BigInteger.ONE);
return a;
I thought the error had somethin to do with only having one class per .java file since the compiler creates a .class file. But how come my first program had two classes and it was OK. Is it b/c the second class was merely a collection of fields, almost like a simple struct in C?
Any help would be appreciated. Thanks

Move the import java.math.BigInteger line to the start of the file.
Use the "[ code ] [ /code ]" tags around your code when you post, it makes reading it a lot easier.

A question about calling classes

Hi,
I have a question regarding software design so that each class is independent of other.
public class A
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             B m_B=new B();
          String strA=m_B.getBString();
          System.out.println(strA);
public class B
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}My question: Is it possible to call the method in class B from class A without creating an instance of class B in method of class A ?
I am trying to figure out if this can be done using interfaces and abstract classes.
I am waiting for some suggestions and if you have completely different suggestion then I am open for it too.
thanks in advance,
@debug.

interface I {
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class B implements I {
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class A {
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public class Main {
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(newbie) Question about replacing .class files and web.xml file

I'm new to servlets and I have two quick questions...
Do I absolutely need a web.xml file to define all my servlets, or can I simply place .class files into the WEB-INF directory and expect them to run?
If my application server (for example Tomcat) is running and I replace a servlet .class file, do I need to restart the server for the new .class file to take effect?
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Hi,
From an article I read:
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A servlet could be accessed by simply using an url like this one:
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With Tomcat 4.x the Jakarta developers have decided to stop allowing this by default. The <servlet-mapping> tag that sets this mapping up, has been commented inside the default web application descriptor (web.xml), located under $CATALINA_HOME/conf:


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A question about Abstract Classes

Hello
Can someone please help me with the following question.
Going through Brian's tutorials he defines in one of his exercises an 'abstract' class as follows
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if the above is correct then it seems odd that the abstract class would be hosted, unless (and this is the only way it makes sense to me) that ultimately (apart from singleton classes) any class that is going to end up being discovered and
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Is that how it is?
Any advise most welcome, thanks
AAnotherUser__
AAnotherUser__

Hi,
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http://OpsMgr.ru/

Question about extending classes

Hi
I've created my own class that extends javax.swing.JTextField as follows:
public class myTextField extends javax.swing.JTextField{
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     protected void initialize()
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          super.setHorizontalAlignment(javax.swing.JTextField.LEFT);
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My question is: Is it possible to have more than one definition in this class?
For example, a myTextField2 that extends JTextField with completly different attributes (eg, different back ground colour etc) or do I have to create a new class?

For example, a myTextField2 that extends JTextField
with completly different attributes (eg, different
back ground colour etc) No, but you can create another constructor that accepts different arguments.
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Question about multiple classes and Linked Lists

Lets say you have 4 classes: LinkedList which is the main class, Node, Card, and Hand. im not putting any constructors yet
The card class keeps track of a card such as a king of diamonds:
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string suit;
string rank;
the node class has a Card object and another node object so it would be
public class Node {
Card c;
Node next;
the hand class keeps track of the users hand. This program will ask the user if they want to add, remove, print out the hand, or print out the score of the hand, I guess it would be like this
public class Hand {
Node head;
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here is an example of Card and Hand ...
not saying its good design
but it does work
public class Cards {
public static void main(String[ ] args) {
Card c1 = new Card ("ace", "diamonds");
Card c2 = new Card ("two", "spades");
Card c3 = new Card ("three", "hearts");
Hand a1 = new Hand ();
a1.add(c1);
a1.add(c2);
a1.add(c3);
System.out.println("\nshowing hand ...");
a1.show();
System.out.println("\ndeleting " + c2.num + " " + c2.suite);
a1.del(c2);
System.out.println("\nshowing hand ...");
a1.show();
} // main
} // class
class Hand exists in 3 states
and is designed to be a chain of cards ...
1. when class Hand is first created
   a. it has no card
   b. and no nextHand link
2. when somecard is added to this Hand
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   b. and the nextHand link is null
3. when somecard is attempted to be added to this Hand
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   b. and the Hand has a nextHand
class Hand {
public Card acard;
public Hand nextHand;
public Hand () {
acard = null;
nextHand = null;
public void add (Card somecard) {
if (acard == null) {
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if (nextHand == null) nextHand = new Hand();
nextHand.add (somecard);
delete this Hand by making this Hand
refer to the next Hand
thus skipping over this Hand in the nextHand chain
for example, removing Hand 3 ...
1 - 2 - 3 - 4   becomes
1 - 2 - 4
public void del (Card somecard) {
if (acard == somecard) {
    if (nextHand != null) acard = nextHand.acard;
    else acard = null;
    if (nextHand != null) nextHand = nextHand.nextHand;
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nextHand.del(somecard);
public void show() {
if (acard == null) return;
System.out.println(acard.num + " " + acard.suite);
if (nextHand != null) nextHand.show ();
} // class
class Card {
public String num;
public String suite;
Card (String num, String suite) {
this.num = num;
this.suite = suite;
} // class

Question about PickMouseBehavior class

Hello, I wrote yesterday in this forum, but now my problem is other. I'm doing a extension of PickMouseBehavior class, but I want that these class is only activated with a specific mouse button or when I passing the mouse over determinated Box element(Box is my branchgroup for the PickMouseBehavior class).
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Sorry about my bad english.
Thanks

i think is in the Class class. I'm not so sure as don't have the API on this machine. You can get the class from every object from the getClass() method, then call the getResource() or getResourceAsStream() i can't really remember...

Question about a Class loading error

how can we obtain to reduce the size of classes throughout run time as the source code of my project alone is about 8 MB and this is too heavy for a me program.
so anybody has any suggestions?

I see thanks.
Did you consider keeping that data outside of device (at some web server)? That way, MIDlet would be installed without it and later would download the data from web. Download, in turn, can be done either every time it is needed, or once at MIDlet first launch - in the latter case, downloaded data could be stored in rms for next time it is needed.
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Hi, guys. I'm green hand and here are two questions puzzled me several days.
We know such example as below is a case of cyclic inheritance
class Base extends Base{
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class Base{
class Derived extends Base{
class Base{
I can't find the clue of cyclic inheritance. It's quite different from the case that a class extends itself or its subclass.
Another question is why the inner class can't have the same name of outer?
class Base{
class Base{
The compiler says Base is already defined in unnamed package. As it says, the inner class is defined in the
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class Base{
class Basic{
class Derived {
class Basic{
We know it's correct. But as the compiler says above, the different two inner class Basic are both defined in the
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Hi,
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Regards,
Sandeep

Question about handing classes in Objective-C

Greetings -- I'm pretty new to Objective-C. I do have a few apps out in the app store, but they were simple one-form apps where I was able to dump everything into the main class and be happy with it.
This new project I'm working on, is huge in comparison. Over 25 views, accessible through TableView driven menus.
I was able to get all of the menus working, each launching a separate view NIB file (so far, just a label to show me that it's done, but I got that part working.)
Now what I'm trying to do, is add a "click" sound when a row is selected. But I'm wanting to do this in a separate class, so each .m file can instantiate it's own version of the logic instead of having the same code 29 times.
So, this is what I've done:
Click.h
#import <Foundation/Foundation.h>
#import <AudioToolbox/AudioToolbox.h>
@interface Click : NSObject
SystemSoundID soundID;
-(void) playClick;
@end
Click.m
#import "Click.h"
@implementation Click
-(id) init
self = [super init];
NSString *path = [[NSBundle mainBundle] pathForResource:@"click" ofType:@"wav"];
AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath:path], &soundID);
return self;
-(void) playClick
AudioServicesPlaySystemSound (soundID);
@end
RootViewController.h
#import <UIKit/UIKit.h>
#import "Click.h"
@interface RootViewController : UITableViewController <UITableViewDelegate, UITableViewDataSource>
NSArray *controllers;
Click *clicker;
@property (nonatomic, retain) NSArray *controllers;
@property (nonatomic, retain) Click *clicker;
@end
RootViewController.m
#import "RootViewController.h"
@implementation RootViewController
@synthesize controllers, clicker;
- (void)viewDidLoad
Click *newClicker = [[Click alloc] init];
clicker = newClicker;
[newClicker release];
self.title = @"Main Menu";
- (void)dealloc {
[controllers release];
[clicker release];
[super dealloc];
#pragma mark Table View Delegate Methods
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
[clicker playClick];
I cut out the code pieces regarding the TableView that I know works, and tried showing only the parts that I've added to make the sound.
What I've tried, is when the RootViewController is created, it has a SystemSoundID type variable defined with it named clicker. Then as part of "viewDidLoad", instantiate an instance of the class and have it automatically populate the variable "soundID". Then during "didSelectRowAtIndexPath", I want the "playClick" method of "clicker" to be run, but at this point the app seems to get caught in some sort of perma-loop, and I have to "STOP"/"Home" out of it.
I'm hoping the problem is my rookie-status at using Objective-C objects, and the solution jumps out at you veterans, and then whatever problem I am having won't be duplicated when I create additional classes that I'd want to merge into my ViewController logic.
Hope I've made everything clear. If anyone has questions, I'll be checking for replies
Thanks.

Dragon's Nest wrote:
Is it preferred to init a copy and assign it like you did above?
Yes, it's an accepted pattern which you'll see in most of the sample apps. Asnor's code works just as well in this case, and it might always work for you if you stick to that same pattern. However if you were working on a team and everyone else used the more common pattern it might cause a problem. For example, this code would cause a memory leak:
@property (nonatomic, retain) Click *clicker; // interface
self.clicker = [[Click alloc] init]; // implementation
The above is the flip side of your original code. In this case, because we're not releasing the newly alloced object, its retain count is +2 after the setter retains it.
There are other advantages to the accepted pattern. Suppose you weren't assigning the new object to an ivar but only using the object in that one block of code. Should you then release it? Yes. Will you remember? Well, if you're using the pattern, you'll always release it. If you always release the local pointer regardless of whether it gets retained elsewhere, you're much less likely to have a memory leak. How bout the case where you return the pointer (i.e. alloc an object and return it's address from that method)? In that case you just autorelease it. So whoever called the method needs to retain the returned object if it needs to be used after the current event cycle.
Either way, immediate release or autorelease, you're always releasing an alloced object in the same block of code.
Memory management can easily get out of control without following consistent patterns. Alloc->retainBySetter->release is the accepted pattern for Cocoa. Your original code meant to use the correct pattern, but you just forgot that clicker=object isn't the same as self.clicker=object because the latter retains the object. Once you've consistently used the correct pattern for awhile, you'll almost never make that mistake.
Also, is there any difference in calling it in the following two ways:
@property (nonatomic, retain) Click *clicker; // <-- must be considered to answer this question
@synthesize clicker;
[clicker playClick];
[self.clicker playClick];
In the above case there's no difference since the getter synthesized for that property declaration will simply return the value of the ivar (i.e. the address of the retained Clicker object). But in the general case, there certainly could be a difference. If the property was atomic, for example, the results could be different. Of course there will definitely be a difference if you wrote a custom getter that did something more than the default.
Is there a rule or convention re when to use the getter and when to use the ivar directly? Not that I know of. I think you just need to be aware of what the getter does when deciding whether to use the dot notation. This is a point you might want to research a little more, though. Maybe someone here with more experience in Obj-C or Cocoa will comment.
In fact a few of the experts in this forum advise against ever using dot notation. They feel it was invented to crash newbie programs. If you never use dot notation the difference between these two lines is much easier to see:
clicker = newClicker;
[self setClicker:newClicker];
But once again, if you stick to the same pattern all the time, it's much harder to make a mistake.
- Ray

Question about nested classes

Hi, i currently have the following problem:
I have 2 classes, one of which also has a nested class:
1. Home.java (extends JApplet)
2. Away.java (extends JPanel) has nested class, private class ButtonListener implements ActionListener
Now in Home.java I have a Vector ( called bankaccount) which i pass to the Constructor of Away.java ( I declared the vector again there as an instance by Private Vector bankaccount;).
My problem is that in ButtonListener I am trying to access the Vector so that i can modify it when a button has been clicked, and i thought i could just use the commands of bankaccount.add() and bankaccount.get() directly, however it seems like ButtonListener cannot access the Vector, even though i passed it along to the Constructor of the Away class.
Any suggestions on how i get access the Vector from the ButtonListenere class?

This is an example:
public class Home extends JApplet
private Away away;
private Vector bankaccount;
public void init()
     bankaccount = new Vector();
     away = new Away(bankaccount);
public class Away extends JPanel
private Vector bankaccount;
JTextArea text1= new JTextArea(50,50);
public Away(Vector bankaccount)
   //declare buttons,textarea,setLayout,etc
button1.addActionListener (new ButtonListener());
//i can set text1.setText(( String)bankaccount.get(0));
// here to access bankaccount, and it shows up fine, but i want
// do it in from the class below
private class ButtonListener implements ActionListener
          public void actionPerformed(ActionEvent event)
                     //trying to access bankaccount here by doing:
                    // but it is not doing anything
                    text1.setText(( String)bankaccount.get(0));
}

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