The Template Method design pattern solves problems like:
How can the invariant parts of a behavior be implemented once
so that subclasses can implement the variant parts?
How can subclasses redefine certain parts of a behavior
without changing the behavior's structure?
See Applicability section for all problems Template Method can solve. See Solution section for how Template Method solves the problems.

• The standard way is to define subclasses (SubClass1|operation()) that redefine the behavior of a parent class (Class|operation()).
• This makes it impossible to redefine only certain parts of the behavior independently from (without having to duplicate) the other parts.
• That's the kind of approach to avoid if we want that subclasses can redefine only certain parts of a behavior without changing the other parts or the structure of the behavior.
• For example, designing reusable classes.
  It should be possible that a class implements the common (invariant) parts of a behavior and let users of the class write subclasses to redefine the variant parts to suit their needs. But subclasses should not be able to change anything else.
• For example, enforcing invariant parts of a behavior.
  A behavior often requires invariant functionality to be performed before and/or after its core functionality (for example, for setting up and resetting state).
  It should be possible to redefine only the core functionality without changing the invariant functionality.