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Showing posts from November, 2011

Servant (Design Pattern) in Java - example

The servant design pattern - or better idiom is used to provide the functionality (methods) to some group of objects. This functionality is common for all these object and therefor should not be repeated in every of these classes.
The object, which should be served is passed to the method of servant as a parameter. All the served objects should implement common interface - in this particular example IMovable interface. Also the type of argument passed to the servand method is of type IMovable.
The servant in this example is used to move objects from one position to another. In real life application these methods should change the position of object in small steps so that the final change would look like smooth movement (animation). In my servant method, only some message are printed instead for demonstration.
IMovable interface:
package com.shimon.servant; import java.awt.Point; /** * Movable interface * @author shimon * */ public interface IMovable { public void setPosition(P…

Java Crate (design pattern/idiom) example

Another example, based on example explained in the book "Navrhove vzory" (Design patterns) from Rudolf Pecionvsky. I have re-made this example just to somehow get more familiar with this design pattern (or better idiom). The "crate" is used to store the set/list of object in one place, so that the moving (passing) these objects is easier.

The example from the book is very easy, and helps to understand, how this design pattern could be applied to som very usefull application (e.g. day planner)

Code example:
package com.sim.crate.common; import java.util.ArrayList; import java.util.List; import java.util.ListIterator; /** * The Day Plan class demonstrates the usage of crate to create simple day plan, with items that do not collide. * @author shimon * */ public class DayPlan { private final List actions = new ArrayList(); /** * Tries to add an item to the day plan with entered start, end time and duration. Returns true, if * the try was successful, or f…

Immutable object example

After reading some chapters of  the book "Design patterns" (Navrhove vzory) from czech author Rudolf Pecinovsky, I decided to test my own examples of usage of the design patterns mentioned in this book. In this first post I will publish here a code that is an example of usage of the immutable objects.

As you maybe already know - the immutable objects cannot be changed after their creation. That can be very useful in some situation. In this particular example (which is kind of a english copy of the czech example mentioned in the book "Navrhove vzory") the object, which represents fraction and its operations is created. The main thing here is, that during every operation (method) new instance of class Fraction is created instead of modifying the existing Fraction instance.

Immutable objects can be very useful in concurrent applications - their state cannot be changed, so there is no way they could be corrupted by other threads.

Code example:

package com.shimon.immuta…