jquery gets the number of identical sub-elements under an element code_jquery

For example, the following html code needs to get the number of a elements under the P element:

<p id="father"> 
<a></a> 
<a></a> 
<a></a> 
<a></a> 
<a></a> 
…… 
<a></a> 
</p> 

We can write like this:

$("#father a").length