John brewer why a duck

In , John Sr. Consequently, John Jr. After college, he served in the Army, working in a high-security position that took him around Europe. Upon his return, he came back to a place hardly recognizable. However, traveling around the world allowed him to meet an even wider range of people and create even more memories that would help him cultivate the skills needed to be a successful historian.

He identified many of the people in the collection by relying on his own knowledge and conducting more than interviews with residents around the city.

But Brewer possesses an understanding of local history that exceeds the personal. He is the owner of The Greater Pittsburgh Coliseum, a community center and local archive in Homewood that used to be one of four trolley factories.

The duck had set up camp between the stationary right field fence and the gate, and had built a cozy nest of leaves. Brewer has been playing road games and using neutral artificial turf fields when possible, but groundskeepers cannot even get a mower on the soggy outfield. Utterback said he has been in contact with a local game warden who said he would keep an eye on the situation. Utterback said he was hopeful that the field would be playable — ducks permitting — by Friday, when Brewer is scheduled to face Bangor.

The hope is that the eggs will hatch, and the ducks will waddle away to a more suitable location. An Introduction to Polymorphism and Design Patterns. What does it mean to be object oriented? There are 3 key aspects of object oriented programming:. Encapsulation means that objects keep their state information private. Rather than directly manipulating an object's data, other objects send requests to the object, in the form of messages, some of which the object may respond to by altering its internal state.

Polymorphism means that objects of different classes can be used interchangeably. This is especially important, as it allows you to hook up classes at a later date in ways you didn't necessarily foresee when those classes were first designed.

Inheritance means that objects of one class can derive part of their behavior from another base or parent class. You can program using an object-oriented approach in just about any language.

For example in C, you can implement encapsulation with pointers to privately defined structs, polymorphism with function pointers, and inheritance by somewhat trickier use of those same function pointers. An object-oriented programming language makes object-oriented programming easier by making encapsulation, polymorphism and inheritance first-class language constructs, usually through some concept of a "class". This paper deals primarily with polymorphism. Ward Cunningham has said the Polymorphism is the object-oriented programmer's edge.

Just as a downhill skier uses the edges of his skis to quickly turn and react to the changing landscape, an O-O developer uses polymorphism judiciously to produce systems that are simple to understand, yet can be rapidly modified in the face of changing requirements. Here we are saying that we have a class called Duck, and that objects of class Duck know how to quack.

Obviously a production Duck class would have additional methods for things like swim , walk , and fly , but quack is sufficient for our purposes. This is fine, as far as it goes. But now let's introduce another related class into the system, a Duck Call:. A DuckCall is a completely different class that just happens to also know how to quack. So now we can use Duck like:. What we can't do, however, is use a DuckCall where a Duck is expected:. There are occasions where it might come in handy to be able to use Duck and DuckCall interchangeably.

In Java the way you say this is to create an interface, like this:. Essentially, a client of Quackable is saying, "I don't care what you are, as long as you can respond to quack. Now we can refactor Duck1 into Duck2. Note the only change is adding an implements clause to the class declaration.

The actual body of the class is unchanged. Now the client can create a Duck or a DuckCall, and use them interchangeably:. Even though the client no longer needs to know the exact type of a Quackable in order to call its quack method, it still needs to know the type of the object to create it.

There are cases where we would just as soon insulate the client entirely from the underlying implementation class. To do this, we encapsulate the creation of the object in a method on another class. It's called a Factory Method, because it manufactures an instance of the proper class. Now that we have added polymorphism, in the form of the Quackable interface, a large number of patterns become easily reachable.

For instance, suppose we wanted to keep track of the number of times quack was invoked on any Quackable in the system. Rather than modify Duck and DuckCall, we can create a simple wrapper class. This class will implement Quackable, and itself contain a Quackable. When its quack method is called, it will increment the global quack count and then pass the quack call on to its contained Quackable:.

Now, a client just has to wrap each Quackable in a QuackDecorator, and the system will keep an actuate count of the number of times quack was called. We forgot to wrap one of the Quackables in a QuackDecorator!

Our quack count will be off as a result. This is what happens when you force too much creation work onto the client.