In the design pattern study we have to know some vocabulary as:
-Abstraction: a concept or idea not associates with any instance.
-Encapsulation: which is the restriction to access some of the object’s components or bundling of data with the method operating in data
-Polymorphism: Is the ability to create a variable, a function or an object that has more than one form.
-Inheritence: which is an “IS A” relationship generally used as “extends” in OOP.
Design Patterns principles like:
-Identify the aspects of your application that vary and separate them from those what stays the same;
-Program to an interface not to an implementation
-Favor composition over inheritence
The Strategy Pattern defines a family of algorithm, encapsulates each one and makes them interchangeable. Strategy lets the algorithm vary independently from client that uses it.
Here is a small application of this Pattern, The Duck program.
public class FlyingWithWings implements FlyBehavior {
public void fly(){
System.out.println("I am flying with wings");
}
}
public class FlyNoWay implements FlyBehavior {
public void fly(){
System.out.println("I can't fly");
}
}
public interface FlyBehavior {
public void fly();
}
public class Quack implements QuackBehavior {
public void quack(){
System.out.println("I am quacking");
}
}
public class MuteQuack {
public void quack(){
System.out.println("Mute quack");
}
}
public class Squeak {
public void quack(){
System.out.println("I am squeaking");
}
}
public interface QuackBehavior {
public void quack();
}
public abstract class Duck {
FlyBehavior flybehavior;
QuackBehavior quackbehavior;
public void performFly(){
flybehavior.fly();
}
public void performQuack(){
quackbehavior.quack();
}
}
public class MallardDuck extends Duck {
public MallardDuck(){
quackbehavior = new Quack();
flybehavior = new FlyNoWay();
}
public void display(){
System.out.println("I am a real mallardDuck");
}
}
public class MiniDuckSimulator {
public static void main(String[] args) {
Duck mallard = new MallardDuck();
mallard.performFly();
mallard.performQuack();
}
}