Wiki  - Library Entry

Intent

Let a descendant redefine certain tasks without modifying the basic algorithm defined by an ancestor method.

Solution

1.     Break out primitive steps into separate methods in ancestor class.

2.     Construct method for basic algorithm in ancestor that calls the primitive methods.

3.     Override the primitive methods in descendant classes to implement specific tasks.

Consequences

• A fundamental technique for code reuse -- particularly important in class libraries and frameworks to factor our common behavior.
• Leads to inverted control structure called Hollywood Principle (dont call us, well call you.)
• A primitive method in the ancestor may provide a default behavior that descendants may optionally override (called hook methods.)