Is it really useful to preload images with new image?

It is often used to show images alternately on webpages. We recommend that you use new image () to preload images. But is it useful to use new image?
Test:
Put a filter in the background to capture all/* requests:
In dofilter, simply print the request URL:

Code
Httpservletrequest httprequest = (httpservletrequest) request;
System. Out. println ("requets URL:" + httprequest. getrequesturi ());
Chain. dofilter (request, response );

HTML code:
Code<Button onclick = "Change ()"> change </button> <br/>