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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;
    }

    ...
}

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