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Event handling in Java December 19, 2006

Posted by deltawing in Java, Programming.
1 comment so far

Event handling has always confused me. So I’m going to summarise it all here.

//Handling mouse events
public boolean mouseDown (Event e, int x, int y)
{
//code here

    return true;

}

- what is an Actionlistener why is it needed?
- MouseListener? why is it needed

-actionPerformed? getSrc?

If there are several buttons, textfields, etc that need to be handled, use actionPerformed(ActionEvent e)
public void actionPerformed (ActionEvent event) {

String cmd = event.getActionCommand ();

if ( cmd.equals (“A”)){
fPushACount++;
showStatus (event.getActionCommand () +
” pushed ” + fPushACount + ” times”);
}else{
fPushBCount++;
showStatus (event.getActionCommand () +
” pushed ” + fPushBCount + ” times”);
}

} // actionPerformed()

Don’t forget to attach the listeners to the event source (ie buttons or else it wont work)!!

Passing arrays to methods (Java) September 26, 2006

Posted by deltawing in Java.
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This confuses people from time to time. Let’s clear it up now.

to declare an array you do this:

int[] somearray = new int[20];

or if you prefer,
int somearray[] = new int[20] ;

doSomething( somearray ); //when passing an array, do not include the square backets

public void doSomething( int somearray [] ) //when receiving an array, have the brackets in place. Also, do not include the array size in the brackets.

{..}

Dealing With Files & Directories with Java August 30, 2006

Posted by deltawing in Java.
2 comments

Short post:

Had a lab today where one of the exercises was to write a simple application that finds a file in the specified directory. I didn’t know how to deal with files and directories so I went searching online.

A very useful resource that I came across:

http://javaalmanac.com/egs/java.io/TraverseTree.html?l=rel

The almanac has tons of useful resources, just search! :)

Example of a LinkedList August 23, 2006

Posted by deltawing in Computer Science, Java.
2 comments

Here is a very simple example of a LinkedList to get started with:

import java.util.Iterator;
import java.util.List;
import java.util.LinkedList;

public class LinkedListTest
{

public static void main(String[] args)
{

//create a new LinkedList
List list = new LinkedList();

//adding elements to the list. We are adding Strings.
list.add(“i”);
list.add(“like”);
list.add(“to”);
list.add(“code with”);
list.add(“Java 5″);

//the list object calls the iterator() method of the LinkedList to obtain the iterator
Iterator iter = list.iterator();
while(iter.hasNext())
{
System.out.println(iter.next());
}

}

}

—————————————————————————————–

LinkedLists are:

  • Very efficient for inserting and removing elements.
  • Not so fast when accessing elements in order (though not slower than a normal ArrayList)
  • Slow when randomly accessing elements
  • Java 1.5 version supports Autboxing
  • Uses an Iterator object to traverse through the elements
  • Comes in more flavours – Doubley Linked Lists and Circular Linked Lists.

Please, corrections if mistakes have been made!