pradeepscribbles: 2011

Monday, November 7, 2011

List Boxes Selection 2

<html>
<head>
<title>List Boxes Selection </title>
</head>
<body>

<script>

var ListUtil = new Object();

function listBoxMani()
{

alert(" listBoxMani() ");

var oListbox = document.getElementById("selAge");

alert(" oListbox "+ ListUtil.getSelectedIndexes(oListbox));

}

ListUtil.getSelectedIndexes = function (oListbox)
{
var arrIndexes = new Array;
for (var i=0; i < oListbox.options.length; i++)
{
if(oListbox.options[i].selected)
{
arrIndexes.push(i);
}
}
return arrIndexes;
};

</script>

<form name="ListBoxes_form1">

<select name="selAge" id="selAge" size="2" multiple="multiple">
<option value="18-21">18-21</option>
<option value="22-25">22-25</option>
<option value="26-29">26-29</option>
<option value="30-35">30-35</option>
<option value="Over 35">Over 35</option>

</select>

<input type="button" value="getSelectedIndex" onClick="listBoxMani();">

</form>

</body>
</html>

Retrieving the selected option(s)

selectedIndex is an attribute of <select> element which contains the index of selected Index, as we previously saw oListbox.selectedIndex

If selection box type is list box ( list box by setting the multiple attribute of the <select/> element to "multiple") ( not for combo box )means it is possible to select more than one option

if multiple options are selected , by using oListbox.selectedIndex we can get only the first selected item , but that really doesnâ€™t help.

What we need is a way to get the index of all the selected options ,to get the index writing an custom method will solve all the problem

For this, you need a custom method, which is the first for the ListUtil object. The getSelectedIndexes() method takes advantage of another special property of the

List Boxes and Combo Boxes 1

List box and Combo box are created using HTML <select> tag , by default browser renders <select> element as combo box

<html>
<head>
<title>List Boxes and Combo Boxes </title>
</head>
<body>
<script>

function listBoxMani()
{

var oListbox = document.getElementById("selAge");

alert(" oListbox based on Id "+ oListbox.options[oListbox.selectedIndex].getAttribute("value"));

oListbox = document.forms["form1"].selAge;
oListbox = document.forms[0].selAge

}

</script>

<form name="ListBoxes_form1">

<select name="selAge" id="selAge" onchange="listBoxMani();">
<option value="18-21">18-21
<option value="22-25">22-25
<option value="26-29">26-29
o<ption value="30-35">30-35
o<ption value="Over 35">Over 35
</select>

<select name="selAge1" id="selAge1" size="2">
<option value="1">18-21</option>
<option value="2">22-25</option>
<option value="3">26-29</option>
<option value="4">30-35</option>
<option value="5">Over 35</option>
</select>
</form>

</body>
</html>

<select name="selAge" id="selAge" onchange="listBoxMani();">
<option value="18-21">18-21</option>
<option value="22-25">22-25 </option>
<option value="26-29">26-29 </option>
<option value="30-35">30-35 </option>
<option value="Over 35">Over 35 </option>
</select>

Here the above code render an combo box, The value attribute of each

Tuesday, May 10, 2011

Drag and Drop

Here is example code for drag and drop

<html>
<head>
<title>Drag and Drop Example </title>
<script type="text/javascript" src="EventUtil.js"> </script>
</head>
<body>
<div id="myDiv1" class="draggable" style="background:red;width:100px;height:100px;position:absolute"></div>
<div id="myDiv2" class="draggable" style="background:blue;width:100px;height:100px;position:absolute;left:100px"> </div> <div id="myDiv3" class="draggable" style="background:green;width:100px;height:100px;position:absolute;left:200px"> </div>
<div id="myDiv4" class="draggable" style="background:yellow;width:100px;height:100px;position:absolute;left:300px"></div>

<script type="text/javascript">

var DragDrop = function(){

var dragging = null;

function handleEvent(event){

//get event and target
event = EventUtil.getEvent(event);
var target = EventUtil.getTarget(event);

//alert(" target "+ target);
//determine the type of event
switch(event.type){
case "mousedown":
if (target.className.indexOf("draggable") > -1){
dragging = target;
}
break;

case "mousemove":
if (dragging !== null){

//get event
event = EventUtil.getEvent(event);

//assign location
dragging.style.left = event.clientX + "px";
dragging.style.top = event.clientY + "px";
}
break;

case "mouseup":
dragging = null;
break;
}
};

//public interface
return {
enable: function(){

EventUtil.addHandler(document, "mousedown", handleEvent);
EventUtil.addHandler(document, "mousemove", handleEvent);
EventUtil.addHandler(document, "mouseup", handleEvent);
},

disable: function(){
EventUtil.removeHandler(document, "mousedown", handleEvent);
EventUtil.removeHandler(document, "mousemove", handleEvent);
EventUtil.removeHandler(document, "mouseup", handleEvent);
}
}
}();

DragDrop.enable();

</script>
</body>
</html>

Here at two methods DragDrop:enable() and disable(), is used which provides additional attach and detach all events , and provide addtional measure of control over the dragdrop functionality

here to start DragDrop for an object enable function has to be called , which in turn call EventUtil.addHandler , after which if any move event occurs [mouseup, mousedown,mousemove] in that page means it is captured in handleEvent

In handle event if mousedown is clicked over an div with the class draggable and moved means , X

In this example, an element ’ s left and top coordinates are set equal to the event object ’ s clientX and clientY proper ties, which places the element at the cursor ’ s position in the viewport. The effect is an element that follows the cursor around the page whenever it ’ s moved. that is how DragDrop works

when mouse is released dragging variable is cleared, for implementing DragDrop functionality the object should be in the absolute position

ps: source: Wrox Professional JavaScriptTM for Web Developers

Events

Events is base for Java script to interact with HTML , Events indicates some type of actions occurs in document or in browser etc,

Dom level 0 Event Handlers

The traditional way of assigning event handlers in Java script is to assign a function to an Event handler property, This was the events handler assignment method introduced in the fourth generation of web browser and still remains in all modern browser due to its simplicity and cross browser support. to assign an event handler to Java script , you must first retrieve a reference to the object to act on , each element has event handler properties the are typically all lowercase , such as onclick , An event handler is assigned by settings the property equal to a function as in this example

<html>
<body>

<div id="myBtn"> Click Here </div>

<script>
var btn = document.getElementById("myBtn");
btn.onclick = function()
{
alert(this.id); //"myBtn"
alert(this.innerHTML);
};

</script>

</body>
</html>

Dom level 2 Event Handler

DOM level 2 Events defines two methods to deal with assignment and removal of Events handlers
addEventListeners() and removeEventListener() . These methods exist on all DOM nodes and accept
three arguments : the event name to handler function and a Boolean value indicating whether to call the event handler during the capture phase (true) or during the bubble phase , Each element has event handler properties that are typically all the lowercase such as onclick, An event handler is assigned by setting the property equal to a function as this example

<html>

<div id="myBtn"> Click Here </div>

<script>

var btn = document.getElementById("myBtn");

btn.addEventListener("click", function()
{
alert(this.id);
}, false);

btn.addEventListener("click", function(){
alert("Hello world!");
}, false);

</script>

</body>
</html>

ps: source: Wrox Professional JavaScriptTM for Web Developers

Thursday, May 5, 2011

Multiple Column Sort

Here i have given the code of Multiple Column Sort

<html>

<head>
<script>

function generateCompareTRs(iCol,sortType)
{
return function compareTRs(oTR1, oTR2)
{
var sValue1 = oTR1.cells[iCol].firstChild.nodeValue;
var sValue2 = oTR2.cells[iCol].firstChild.nodeValue;

if(sortType=='Desc')
{
return -sValue1.localeCompare(sValue2);
}
else
{
return sValue1.localeCompare(sValue2);
}
};
}
function sortTable(sTableID, iCol)
{
var sorttype = document.getElementById('sortTypeHidden').value;

if(sorttype=='Desc')
{
document.getElementById('sortTypeHidden').value='Asce';
}
else
{
document.getElementById('sortTypeHidden').value='Desc';
}

var oTable = document.getElementById(sTableID);
var oTBody = oTable.tBodies[0];
var colDataRows = oTBody.rows;
var aTRs = new Array;

for (var i=0; i <colDataRows.length; i++)
{
aTRs[i] = colDataRows[i];
}

aTRs.sort(generateCompareTRs(iCol,sorttype));

var oFragment = document.createDocumentFragment();

for (var i=0; i <aTRs.length; i++)
{
oFragment.appendChild(aTRs[i]);
}
oTBody.appendChild(oFragment);
}
</script>
</head>
<body>
<input type="hidden" id="sortTypeHidden" name="Asce">

<table border="1" id="tblSort">

<thead>
<tr>
<th onclick="sortTable('tblSort', 0);" style="cursor:pointer">Last Name </th>
<th onclick="sortTable('tblSort', 1);" style="cursor:pointer">First Name </th>
<th onclick="sortTable('tblSort', 2);" style="cursor:pointer">Third < /th>
</tr>
</thead>

<tbody>

<tr>
<td>Smith </td>
<td>John </td>
<td>A Third </td>
</tr>

<tr>
<td>Johnson </td>
<td> Betty </td>
<td>B Third </td>

</tr>

<tr>
<td>Henderson </td>
<td>Nathan < /td>
<td>C Third </td>
</tr>

<tr>
<td>Williams </td>
<td>James </td>
<td>D Third </td>

</tr>

<tr>
<td>Gilliam </td>
<td>Michael </td>
<td>E Third </td>
</tr>

<tr>
<td>Walker </td>
<td>Matthew </td>
<td>F Third </td>
</tr>

</tbody>
</table>
</body>
</html>

How it works

It works as like as Sorting single column Table

Sorting is done by getting the values of the specified column [dom collections] from the table and storing it to an array then sorting the array values.

Now the tr values are sorted using generateCompareTRs() and stored in a array ,

generateCompareTRs() will return another function compareTRs instead of handling it in one function because In general sorting is done using sort () api , which in turn calls another function generateCompareTRs() , in generateCompareTRs compareTRs function added because

compareTRs is a comparison function

an short note about comparison function
A comparison function is a function with a specific algorithm. It’s helpful to take a look at a basic comparison function before continuing with the explanation:

function comparison_function(value1, value2) {
if (value1 < value 2) {
return –1;
} else if (value1 > value2) {
return 1;
} else {
return 0;
}
};

As you can see, a comparison function compares two values, which is why a comparison function

always has two arguments. If the first argument should come before the second argument, the

function returns –1. If the first argument should come after the second argument, the function

returns 1. If, however, the arguments are equal, the function returns 0. The comparison function

is used in the sort()

As said in desc , comparison function has got only two arguments , but in our case we need two additional argument. The index of the column which is to be sorted and what type of sorting needs to be done(i.e Ascending or Descending Sort ) , so we are constructing a function generateCompareTRs which in turn construct another function compareTRs

And for descending sorting putting a negative sign will do -string1.localeCompare(string2);

Here the sorted values needs to be appended in the table by replacing old tr,

That is done by creating document fragment and adding all the elements (array values) to it

Then appending all child nodes of document fragment back in to the tbody element

ps: source: Wrox Professional JavaScriptTM for Web Developers

Tuesday, April 26, 2011

Sort Table 1

Here i have given the sample code of how Sort table works

<html>
<head>
<script>

function compareTRs(oTR1, oTR2)
{
var sValue1 = oTR1.cells[0].firstChild.nodeValue;
var sValue2 = oTR2.cells[0].firstChild.nodeValue;

return sValue2.localeCompare(sValue1);
}

function sortTable(sTableID)
{
var oTable = document.getElementById(sTableID);
var oTBody = oTable.tBodies[0];
var colDataRows = oTBody.rows;
var aTRs = new Array;

for (var i=0; i < colDataRows.length; i++)
{
aTRs[i] = colDataRows[i];
}
aTRs.sort(compareTRs);

var oFragment = document.createDocumentFragment();

for(var i=0; i < aTRs.length; i++)
{
oFragment.appendChild(aTRs[i]);
}

oTBody.appendChild(oFragment);

}
</script>

</head>

<table border="1" id="tblSort">
<thead>
<tr>
<th onclick="sortTable('tblSort');" style='cursor:pointer;'> Last Name</th>
</tr>
</thead>

<body>
<tr>
<tdA> Smith</td>
</tr>
<tr>
<tdB> Johnson</td>
</tr>
<tr>
<td> C Henderson</td>
< /tr>
<tr>
<td> DWilliams </td>
</tr>
< tr>
<tdE> E Gilliam </td>
< /tr>
<tr>
<td>F Walker </td>
</tr>
<tr>
<td>Z </td>
</tr>
</tbody>
</table>
</html>

How it works

Sorting is done by getting the values of the column [dom collections] from the table and storing it to an array then sorting the array values.

Now the tr values are sorted and stored in a array ,

Here the sorted values needs to be appended in the table by replacing old tr,

That is done by creating document fragment and adding all the elements (array values) to it

Then appending all child nodes of document fragment back in to the tbody element

ps: source: Wrox Professional JavaScriptTM for Web Developers

Friday, April 22, 2011

Thread Safety

Thread Safety is an important Concept in Java, Mainly used in Multi threading programme in case such as When two or more threads need access to a shared resource, they need some way to ensure that the resource will be used by only one thread at a time. The process by which this is achieved is called synchronization. As you will see, Java provides unique, language-level support for it.

Main Purpose in details

For example In a Cinema ticket booking website , there is only one last ticket is available means , in that case two users trying to book the last ticket, two threads are accessing a class for example bookTicket(which is about to book ticket based on availability ), In that case what would happen is same ticket is would be booked for two users(but in reality only one ticket is available in the physical world). To prevent this type of problem a concept called synchronization (That is used in thread safety)

If synchronization is used in that bookTicket() class means only one thread can access the class at a time (booking of same tickets for two users is not possible) others thread has to wait until that thread (which accessed the bookTicket() class first) which enters the class exist

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