Ask the Experts: CQ5 Inheritance Model

Published on by Dan KlcoPicture of Me Dan Klco
This was also posted on: http://labs.sixdimensions.com/blog/dan-klco/2013-08-01/ask-experts-cq5-inheritance-model, however 6D Global Technologies decided to remove my authoring credit, which seems unethical.

In this series of blog posts we pose a question to experts in the Adobe CQ5 platform about Adobe CQ5, Enterprise Content Management and Web Development.

What’s the difference in CQ5’s inheritance model versus standard Java?

The main difference that I can think of is that in standard Java, you will write a class which inherits all the methods of a previous class. These methods can be modified and overwritten, and new methods even added to enhance functionality. In CQ, the inheritance is much more basic. It is based on JSP’s I like to compare the two by thinking of the JSP’s as methods, and the components as classes. Where by default, an empty component with nothing overridden will match exactly the super resource. However, if you add a JSP to your component matching the name of the super resource, that JSP will take precedence over the super resources, allowing you to override smaller portions. — Ryan McCullough, Staff Engineer

They are very similar: they both support single inheritance, and polymorhism. Scripts defined within a “parent” resource may be “overriden” by a child by simply defining the same script. This is very similar in concept to extending a Class and overriding a method by defining the same method name with the same signature. The one thing that CQ5 (Sling implements this, not CQ5) does not support is scoping. There is no concept of Public, Package Protected, Protected and Private. In Sling, everything is Public. Once a Script is defined, ANY Child may override it. — Michael Kelleher, Technical Lead

Like Java, inheritance in CQ is just single inheritance, where there can only be a single super type.  Inheritance in CQ is part of the Sling framework and is done by using the sling:resourceSuperType attribute for setting the super type for a component.  Using the super type, CQ components will inherit parts from the super component such as scripts and dialogs which are not defined in the current component.   If the component inheritance is thought of as similar to Java’s class inheritance, then each script can be thought of as similar to a method.  Overall, the two concepts are pretty similar their main differences are the actual execution and the fact that CQ inheritance does not have any permissions, all scripts can be overridden. — Daniel Klco, Associate Director


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