Java J2ee Planet

In developing applications, we come across components which are individual objects and also can be collection of objects. Composite pattern can represent both the conditions. In this pattern, you can develop tree structures for representing part-whole hierarchies. TThe most common example in this pattern is of a company’s employee hierarchy. We here will also take the same example. The employees of a company are at various positions. Now, say in a hierarchy, the manager has subordinates; also the Project Leader has subordinates, i.e. employees reporting to him/her. The developer has no subordinates. So, let’s have a look at the class Employee: This is a simple class with getters and setters for attributes as name, salary and subordinates. Employee.java package structural.composite; import java.util.Vector; public class Employee { private String name; private double salary; private Vector subordinates; public Vector getSubordinates() { return subordinates...

Facade as the name suggests means the face of the building. The people walking past the road can only see this glass face of the building. They do not know anything about it, the wiring, the pipes and other complexities. The face hides all the complexities of the building and displays a friendly face. This is how facade pattern is used. It hides the complexities of the system and provides an interface to the client from where the client can access the system. In Java, the interface JDBC can be called a facade. We as users or clients create connection using the "java.sql.Connection" interface, the implementation of which we are not concerned about. The implementation is left to the vendor of driver. Let's try and understand the facade pattern better using a simple example. Let's consider a store. This store has a store keeper. In the storage, there are a lot of things stored e.g. packing material, raw material and finished goods. You, as client want access to ...

  The pattern here states about a mechanism by which you can avoid creating a large number of object instances to represent the entire system. To decide if some part of your program is a candidate for using Flyweights, consider whether it is possible to remove some data from the class and make it extrinsic. If this makes it possible to reduce greatly the number of different class instances your program needs to maintain, this might be a case where Flyweights will help. The typical example you can see on this in every book will be of folders. The folder with name of each of the company employee on it, so, the attributes of class Folder are: 'Selected' , 'Not Selected' and the third one is 'employeeName'. With this methodology, we will have to create 2000 folder class instances for each of the employees. This can be costly, so we can create just two class instances with attributes 'selected' and 'not selected' and set the employee's name...

The Adapter pattern is used so that two unrelated interfaces can work together. The joining between them is called an Adapter. This is something like we convert interface of one class into interface expected by the client. We do that using an Adapter. Let’s try and understand this with the help of an example. Again, I will like to take a general example. We all have electric sockets in our houses of different sizes and shapes. I will take an example of a socket of 15 Ampere. This is a bigger socket and the other one which is smaller is of 5 Ampere. A 15 Amp plug cannot fit into a 5 Amp socket. Here, we will use an Adapter. The adapter can be called a connector here. The connector connects both of these and gives output to the client plug which is of 5 Amp. The Adapter is something like this. It will be having the plug of suitable for 15 Amp and a socket suitable for a 5 Amp plug. So, that the 5 Amp plug which here is the client can fit in and also the server which here is th...