Behavioral Patterns : Template Method

Properties:

-          Abstract class defines steps to achieve some task. At some points it defers actions to subclasses.  

-          Common steps are done within abstract class so code repetition is avoided.

-          Subclasses defines subclass specific steps.

Implementation:

-          AbstractClass defines template method in which generic algorithm is formed. At subclass specific points abstract mehods are called to defer specific tasks to subclasses.

-          ConcreteClass extends abstract class and defines abstract methods to implement tasks in a specific way to it.

Java Standard Library Implementations:

-          java.util.AbstractMap  all non-abstract methods.

-          java.util.AbstractList  all non-abstract methods.

-          java.io.InputStream all non-abstract methods.

-          java.io.OutputStream all non-abstract methods.

Example Usage:

abstract class AbstractList {

    // template method: generic algorithm is defined

    public boolean addAll(int paramInt, Collection<? extends E> paramCollection){

         boolean bool = false;

         for (Iterator localIterator = paramCollection.iterator(); localIterator.hasNext(); ) {

           Object localObject = localIterator.next();

           add(paramInt++, localObject);//implementation specific section is deferred to subclasses

           bool = true;

         }

        

        return bool;

    }

    ...

}

class ArrayList {

    // subclass specific section is defined in subclass

    public boolean add(E paramE)

    {

         this.elementData[(this.size++)] = paramE;

         return true;

    }

    ...

}