Expanding the conditions of a task may require the repetition of similar actions in a certain order. Such actions help programmers to execute patterns, or Java Pattern (JP), which automate the creation of objects and their relationships in the user's workspace. Teams can use JP to reduce errors, simplify modeling, and improve performance. Designers create JP using information identified from existing reference implementations and sample solutions.
Design Pattern Structure
Solution teams install Java Design Patterns, using wizards, apply patterns in the workspace. These best-practice wizards reduce the need for coding and complex setup.
Typical JP structure:
- The data model includes all entities and data elements that implement the template in which this data is organized in the workspace. It provides the expected user input and applies it to the workspace, and also has an integrated help system available when the user launches the Java Pattern design.
- User interface. Developers interact with design patterns using the JP Design Wizard. He collects information and organizes it on different pages of the wizard, supplementing with tips or built-in help, at the request of the user.
- Processor implementation. When the user finishes working with the Java Design Pattern wizard and clicks the Finish button, the design pattern applies the data entered by the user to the entities and elements defined in this project. After that, JP generates and organizes objects and data elements in the workspace.
Development cycle sequence
The life cycle of a design pattern begins with the identification and isolation of JP itself. When working with a reference implementation, designers identify a repeatable layout that includes resources and resource relationships with the workspace. The tasks in the life cycle of the Java Pattern design are performed by two different participants, the designer who creates and distributes the layout, as well as the operator who sets up the design patterns and runs JP to facilitate the development of the solution.
Design Processing Sequence:
- The general modeling tasks and key resources in reference implementations, examples of solutions and best practices are evaluated and establish which repetitive tasks can be automated in JP.
- Develop JP using identified resources as key components.
- Test the resulting design patterns by running them in Design Studio.
- Include JP in plugin projects that link to the object project and update site.
- They establish functions depending on their role and goals.
- Design patterns are launched to complete the design decision.
File pattern.xml
Each design template has a “pattern.xml” file that defines the contents of the JP model. In addition to the high-level attributes set for the file, such as namespace, template identifier, and name attributes. In the XML Schema section, this is a file named DesignPattern.xsd in the schema folder that is available in the Design Studio software package. The developer can indicate whether the design pattern is a major or minor release or part of a service pack release by the design pattern version number.
The Introduction page in the wizard contains information that describes how JP can be used. Design Pattern Sections:
- Valid target projects that conserve resources when applying the design pattern.
- Placeholders represent information that must be entered by a user using JP.
- Pages that appear in the wizard. JP tokens are organized as pages in a wizard, where each page is a group of them. You can define any number of token groups.
- A list of resources included in the JP that copies these resources to the user's workspace.
- The default information provided to the JP wizard for automatically populating token names.
Java Design Approach
Design patterns are already defined and provide a standard industry-wide approach to solve a recurring problem, so this saves time if used wisely. The use of design patterns facilitates reuse, which leads to the creation of more reliable and easy-to-maintain code. This helps lower the total cost of ownership (TCO) of the software product and makes code easier to understand and debug. This leads to faster development, and new team members are easily trained in new programs.
Java design patterns fall into three categories — design for creation, structure, and behavior. Creation Design JPs provide a solution to create the object in the best way for specific situations.
The Singleton pattern restricts instantiation of a class and ensures that there is only one class instance in the Java virtual machine. This seems like a very simple JP, but when it comes to implementation, it has a lot of problems. The implementation of the Singleton template has always been a controversial topic among developers and one of the most discussed topics in JP design.
Factory design
Java Factory Pattern is used when there is a superclass with several subclasses. This template takes responsibility for instantiating the class from the client program to the factory class. You can apply the Singleton pattern to the Factory class or make the factory method static. This is one of the most widely used JPs.
An Abstract Factory is similar to a Factory pattern, which returns various subclasses based on the input provided, and uses the if-else or switch statement to achieve this. In the Abstract Factory template, they got rid of the if-else block, left the factory class for each subclass, after which Abstract Factory returns a subclass based on the input factory class.
JP Builder was introduced to solve some problems of Factory and Abstract Factory, when Object contains many attributes. Builder Pattern Java eliminates the problem of a large number of optional parameters and inconsistent actions, providing a way to step by step construct an object and a method that returns the final object.
Structural structure
The adapter design pattern is one of JP structural design and is used for collaboration of two unconnected interfaces. An object that connects to these unrelated interfaces is called an adapter. As an example from real life, you can consider a mobile charger as an adapter, since it takes 3 V to charge the battery, and a regular outlet produces a voltage of 120 V (USA) or 220 V (Russia). Thus, the mobile charger acts as an adapter between the mobile charging outlet and the wall outlet.
JP Composite Pattern is one of the structural design patterns and is used when it is necessary to represent the hierarchy of the part - the whole, to create a structure so that the objects in it are processed the same way.
A diagram is an example from real life, a structure consisting of objects such as a circle, lines, a triangle, and other geometric shapes. When a programmer fills a picture with, say, red, the same color also applies to objects in JP. Here the picture consists of different parts, and they all have the same operation.
Proxy template
The purpose of the proxy template is "Providing a surrogate or placeholder for another object in order to control access to it." The definition itself is very clear, and JP proxy is used when you need to provide controlled access to functionality.
Suppose there is a class that can execute some commands in the system, but if you need to pass this program to a client application, it can have serious problems. The client program may issue a command to delete some system files or change some parameters that are not needed.
The Flyweight design pattern is used when you need to create many class objects. Since each object consumes memory space, which can be critical for devices with a small amount of memory, such as mobile devices or embedded systems, JP with a simplified design can be used to reduce the memory load by sharing objects. The Java string pool implementation is one of the best examples of Flyweight template implementations.
JP Facade is used to help client applications easily interact with the system. Suppose there is an application with a set of interfaces for using the MySql / Oracle database to create various types of reports, such as an HTML report, a PDF report, and others. Thus, the user will have a different set of interfaces for working with various types of databases.
The client application can use these interfaces to obtain the necessary database connection and report generation. But when complexity increases or interface behavior names are confusing, it will be difficult for the client application to manage it. In this way, they use the Facade template and provide a wrapper interface on top of the existing one to help the client application.
Interface Hierarchies
When a user has hierarchies of interfaces in both interfaces, as well as implementations, then JP "Bridge" is used to separate the interfaces from the implementation and hide implementation details from client programs. Like the adapter template, this is one of JP structural design. The JP implementation of Bridge follows the idea of choosing Composition over inheritance.
JP "Decorator" is used to change the functionality of an object at runtime. At the same time, other instances of the same class will not be affected by this, so an individual object gets changed behavior. JP "Decorator" is one of the structural design patterns and uses to implement abstract classes or interfaces with the composition.
Users use inheritance or composition to extend the behavior of an object, but this is done at compile time and applies to all instances of the class. You cannot add any new functionality during template execution.
Java Regex Pattern Regular Expressions
Applications often require text processing for features such as word search, email validation, or XML document integrity. This often involves pattern matching. Languages such as Perl, sed, or awk improve pattern matching with regular expressions, character strings that define patterns used to find the appropriate text. Pattern matching using the Java programming language required the use of a StringTokenizer class with many charAt substring methods for reading characters or tokens for text processing. This often leads to complex or "dirty" code.
For programmers, it is better to use regular expressions with the java.util.regex package, using the following common scripts as examples:
- Simple word replacement.
- Email verification.
- Removing control characters from a file.
- Search for files.
In order to compile the code in these examples and use regular expressions in applications, you will need to install J2SE version 1.4.
Team communication implementation
The command template is used to implement the loss of communication in the request-response model. In it, the request is sent to the caller, and invoker passes it to the encapsulated command object. The command object passes the request to the appropriate Receiver method to perform a specific action.
Suppose you want to provide a file system utility with methods for opening, writing, and closing a file, and it must support several operating systems, such as Windows and Unix. To implement the File System utility, first of all, you need to create receiver classes that will actually do all the work. Since encoding is performed in terms of Java interfaces, there may be a FileSystemReceiver interface and its implementation classes for various varieties of the operating system, such as Windows, Unix, Solaris, and others.
JP "Translator" is used to determine the grammatical representation of the language and provides an interpreter for working with grammar. The best example of this pattern is the Java compiler, which interprets the Java source code in byte, understandable for the JVM. The Google Translator is also an Example Patterns Java interpreter where input can be in one language and output can be in another.
JP "Visitor" is used when you need to perform an operation on a group of objects of the same type. Using it, you can move operational logic from objects to another class. For example, a shopping basket, in which you can add various types of goods, when the "Place an order" button is clicked, then the total amount payable is calculated.
Java Util Regex Pattern Example
Compilation from a Unix / Linux shell script is used when circumstances arise when a developer does not have an “Ant” or “Ant-based” project to compile custom Java programs. In such cases, they usually use the Linux shell script to compile their Java classes. A very good use that the script makes for the user is to dynamically include all the Jar files that are needed in the classpath. So the jar files are there, compiling them is very simple from the command line.
The program makes two assumptions:
- The user is in a directory above the level with the name "src", which contains the "java" files.
- The user is in a directory above the level with the name "lib", and all the "Jar" files that the program needs are in that directory.
Script Pattern Compile Java.
The regular expressions in Java Util are the use of the Pattern and Matcher classes. You can use the String.matches () method to perform the mapping. In some cases, you need to use a slightly more verbose way to conduct a session, but one that ultimately gives more flexibility and can improve performance. In particular, two classes of the java.util.regex package are used: Pattern and Matcher. Photos are presented below.
The Java Regex Pattern procedure is as follows:
- Compile the expression into a Pattern object.
- The static method Pattern.compile () is called, passing the expression. This method returns a Pattern object. The execution of this object is an internal representation of the template in a form that makes it efficient to perform mappings.
- Whenever you need to perform a match, create a Matcher object.
- In order to check whether a particular line of the template matches, impose the agreement () of the method on the template of the object, passing in the line.
- A Java Pattern Matcher is called, which returns a boolean value indicating whether the string passed to method () matches the regular expression.
Thus, design patterns are very popular among software developers because they present a well-described solution to a typical problem. These are assistants who automate complex repetitive tasks and allow team members with different levels of training to complete them.