Question

I’m studying for an exam, and this was on an old test:

Given:

public interface Interface1 {

    void method1();

    void method2().

}

Show the Decorator pattern class for the interface.

What is it, and does anyone have any resources on where I can learn more about this?

Answer 1

http://www.javacamp.org/designPattern/decorator.html

http://en.wikipedia.org/wiki/Decorator_pattern

The decorator pattern can be used to
make it possible to extend (decorate)
the functionality of a certain object
at runtime, independently of other
instances of the same class, provided
some groundwork is done at design
time. This is achieved by designing a
new decorator class that wraps the
original class. This wrapping could be
achieved by the following sequence of
steps:

1. Subclass the original “Component” class into a “Decorator”
   class (see UML diagram);
2. In the Decorator class, add a Component pointer as a field;
3. Pass a Component to the Decorator constructor to initialize
   the Component pointer;
4. In the Decorator class, redirect all “Component” methods to the
   “Component” pointer; and
5. In the ConcreteDecorator class, override any Component method(s) whose
   behavior needs to be modified.

for your example

public interface Interface1 {

    void method1();

    void method2().

}

public SimpleInterface implements Interface1 {

    void method1() {
        //method1 actions
    }

    void method2() {
        //method2 actions
    }

}

abstract decorator class

abstract class InterfaceDecorator implements Interface {
    protected InterfaceDecorator decoratedInterface;

    public InterfaceDecorator (Interface decoratedInterface) {
        this.decoratedInterface = decoratedInterface;
    }

    void method1() {
        decoratedInterface.method1()
    }

    void method2() {
        decoratedInterface.method2()
    }
}

concrete decorator class

class Method1InterfaceDecorator extends InterfaceDecorator {
    public Method1InterfaceDecorator(Interface decoratedInterface) {
        super(decoratedInterface);
    }

    void method1() {
        decoratedInterface.method1();
        method3()
    }

    void method3() {
        //method3 actions
    }
}

usage:

public static void main(String[] args) {
    Interface simpleInterface = new SimpleInterface();
    Interface decoratedInterface = new Method1DecoratedInterface (new SimpleInterface());

    // These two method1 calls will behave differently
    simpleInterface.method1();
    decoratedInterface.method1();
}