Image caching with html, JAVA Programming

In the airplane program, you may have noticed that the loading of each image appears to be jerky, erratic, or slow, and that the URL for each image flickers in the status bar each time the image changes. This happens because JavaScript does not save a copy of the image in memory that can be used whenever necessary. Instead, each time a different image is loaded by an element, JavaScript must open or reopen the image from its source. You probably accessed the airplane image files directly from the Data Disk on your local computer, and if you have a particularly fast computer, you may not have noticed a loading problem. If you did notice erratic loading of the images, then you can imagine how erratic and slow the animation would appear if you had to download the images from the Web server each time they are loaded. A technique for eliminating multiple downloads of the same file is called image caching. Image caching temporarily stores image files in memory on a local computer. This technique allows JavaScript to store and retrieve an image from memory rather than download the image each time it is needed.

Images are cached using the Image() constructor of the Image object. The Image() constructor creates a new Image object. There are three steps for caching an image in JavaScript:

1. Create a new object using the Image() constructor.

2. Assign a graphic file to the src property of the new Image object.

3. Assign the src property of the new Image object to the src property of an element.

In the following code, the src attribute of the element named myImage is initially set to an empty string "". In the script section, a new Image object named newImage is created. The newImage object is used to save and access the memory cache containing the image file. A file named graphic.jpg is assigned to the src property of the newImage object. The src property of the newImage object is then assigned to the src property of the element.

Be sure to understand that in the preceding code, the graphic.jpg file is not assigned directly to the src property of the element. Instead, the newImage object is assigned to the src property of the element. If you assigned the graphic.jpg file directly to the src property of the element using the statement document.myImage.src = "graphic.jpg";, then the file would reload from its source each time it was needed. The newImage object opens the file once and saves it to a memory cache.

The following code shows a version of the unicycle animation code modified to use image caching. The lines that add each image file to the unicycle[] array have been replaced by a for loop, which assigns a new object to each element of the unicycle[] array until the loadImages variable is greater than the length of the array. In the while loop, each object in the unicycle[] array is assigned an image file using the src property. In the turn() function, the unicycle[curUnicycle] operator in the statement document.images[0].src = unicycle [curUnicycle]; now includes the src property so that the statement reads document.images.

Posted Date: 2/26/2013 5:02:49 AM | Location : United States







Related Discussions:- Image caching with html, Assignment Help, Ask Question on Image caching with html, Get Answer, Expert's Help, Image caching with html Discussions

Write discussion on Image caching with html
Your posts are moderated
Related Questions
Draw: loops through the list of cards drawing them in a single row starting from the screen position referred to by the 'x' and 'y' fields of the Hand class. You can limit the numb

Wechat and SugarCRM Project Description: Seeking the partner able to develop wechat program to integrate with SugarCRM. Wechat Official Account able to perform some functi

I can''t figure out how to do this question: "Given two linear equations: ax + by + c = 0 and dx + ey + f = 0" solve for x and y. A, b, c, d, e, and f being inputted from the user.

Project Description: I want to create similar site: fifacointrader I want similar site like fifacointrader.com Skills required are HTML, Java, PHP, Website Design, Wordpre

What will be the output of this programme? Write comments where you find "//" symbol in the following code? function doSomething() { // 1 setTimeout('doSomething()',10000

how much it will cost me

Need to develop a 3D rolling alarm clock (Android) Project Description: I want an android app as 3D rolling alarm clock It should have sound effect when setting the alarm

Why the number of temporary workers is on the rise? Discuss main reasons? Temporary workers: Temporary workers are those workers that a company can hire to perform a certain ta

write complete application to play game tictactoe

What Is a Socket in Java Networking and RMI? Ans) A socket is one end-point of a two-way communication link among two programs running on the network. A socket is bound to a por