Today, programming in Java, most likely, will not surprise anyone. The progress in this area is so great that our familiar reality would have seemed 50-60 years ago to be a real storyline from the movie a la "Back to the Future".
The origins of the Java language
Java is an object-oriented programming language that was originally developed by Sun Microsystems, and later Oracle began to support and develop it.
Do not confuse a development language with a runtime or software platform. The latter should be understood as a combination of many different components that together ensure the execution of Java code in various hardware environments. Programs written in Java are translated into a special format called bytecode, which is later executed by the
virtual machine (JVM) - part of the software platform.
Installation and getting started
In order to successfully run applications developed in this language, you must install a special package of Java components, which is available on the official Oracle website. The company provides various distributions that differ in the target platform, as well as their various options. The average user does not have to use a different version of Java from the latest, newest. This makes sense only for developers who need features and capabilities specific to specific strategies.
To install Java on your computer, the user must first make sure that the hardware specifications meet the minimum system requirements. Oracle engineers have worked hard to lower the threshold for system requirements, but there is still one that needs to be reckoned with. The user must find the distribution kit he needs on the site, based on the operating system in which he wants to install the software. For example, Java for Windows 7 It is an executable .exe file that will only need to specify a directory for installation, and then it will do everything by itself. It is worth noting that only one copy of the software shell can be installed in the system at a time. Therefore, before installing, you need to make sure that the previous version of Java is removed from the system. If this is not done, the installer will ask you to remove the conflicting program before continuing with the installation.
Start Java development
After the user has successfully installed the software environment, various tools will be available to him both for the execution of already written programs and for creating his own. In order to start programming in the Java language, no additional programs are needed. All you need is a desire to learn new things and understand the architecture of the language. If the user was able to successfully install Java, and in the process there were no conflicts with other programs, then the code can begin to be written in any text editor.
Oracle has taken care to provide the maximum set of tools for developers. The Java package includes a language compiler (Javac utility), which, taking the path to any text file as an argument, converts it into byte code that is understandable to the virtual machine.
After that, the user still cannot start the application and see the results of his work. In order to install the Java application for Windows 7, it must be “packed” into the JAR archive.
The JAR format came from the abbreviation Java Archive, and this is a special kind of the familiar ZIP archive that additionally contains a description of classes and dependencies and points to the entry point (main class) in the application. To create a .jar archive, the utility of the same name is used, which is also included in the standard package from Oracle. After its successful execution, the user can start the created application either by the Java command from the command line or console, or by a simple double click.
Core Java components
In order to successfully develop Java applications, you need to start learning it from the very beginning. Novice programmers sometimes find it difficult to understand the term “object-oriented” language. Many people mistakenly believe that it means the fact that all entities that can be operated on in a language are objects. However, this is not quite true. In Java, in addition to objects, there is also a set of primitive types. These are integer data types (byte, short, int, long), which are integers of different lengths, fractional data types (float, double), as well as strings and character types (String and char), respectively.
For each of them, there are so-called classes - wrappers that are used to create a link to an object of a certain type. This is true for all primitive types except string data.
Java String Class Implementation Features
Java strings are a special class. It can be classified as an immutable object. If we represent the application memory as a heap, which contains an arbitrary string, then each operation on it (selecting a substring, concatenation, replacing characters, etc.) will create a new instance of the original string, which will differ from the original as a result of the operation.
Therefore, you should always work with strings with extreme caution: despite the fact that garbage collection in memory works great, the programmer must be extremely careful not to overflow the memory with unnecessary string references. Fortunately, for this there are many auxiliary classes. For example, you can use StringBuilder and StringBuffer, which allow you to manipulate strings but do not create a new instance after each operation.
Java language - regular expressions. Their appearance and purpose
Regular expressions appeared in the late twentieth century and revolutionized electronic word processing technologies.
Previously, searching for specific sections in a text or substring was a common problem that required effort and time to implement. Programmers had to check almost every section for exact compliance with a given search parameter or compare it with a large number of conditions. However, with the advent of regular expressions, it became possible to use metacharacters, with the help of which it became possible to describe the pattern by which the search should be carried out. In Java, regular expressions appeared in version 5, and have since become an integral attribute of the software environment.
Regular Expression Features in Java
In the Java language, all classes that are somehow used to work with regular expressions are made in a separate package called java.util.regex. In Java, regular expressions are described by the Pattern class, which means “pattern” in English. This class takes as a constructor argument a string that can be used to create the template. When you want to describe it, instead of simple letters, it is better to use metacharacters.
In order to correctly specify the search parameters, it is better to familiarize yourself with the official documentation from Oracle, since many metacharacters may not mean at all what an ordinary user or a novice programmer might think. For example, the “+” sign indicates that one or more instances of the immediately preceding element fall under the template. When implemented in Java regular expressions, special characters are the same as in any other programming language. Therefore, migration from another platform should be painless.
Possible Regular Expressions
It is worth noting that the capabilities of regular expressions are most suitable for processing very large texts. For example, the search for a key or phrase in a book, provided that the register in which the key is written is not important. Manual search of the text to solve such a problem would be extremely inefficient, and with the help of regular expressions built into Java, the problem can be solved with a couple of lines of code.
That is why, when studying the language we are considering, one should not miss such an important section as regular expressions. In Java, they can find application in a wide variety of fields - from checking the correctness of entering data in the form (mail addresses, credit card numbers) to analyzing traffic and user requests.